Urine turbidity chart

Urine turbidity chart DEFAULT

Freshly voided urine is clear and transparent. Cloudy urine may be caused by crystals, deposits, white cells, red cells, epithelial cells or fat globules. Further evaluation with centrifugation, microscopic examination, heating or with ether generally determines the cause of the turbidity.

Substances that cause cloudiness but that are not considered unhealthy include mucus, sperm and prostatic fluid, cells from the skin, normal urine crystals, and contaminants such as body lotions and powders.

Causes of Turbid Urine

References and Links

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Urine Physical Examination, and Interpretation

Urine Analysis

  • These are the normal constituents and findings in the normal urine.
  • Routine urinalysis includes:
    1. Physical character.
    2. Chemical analysis.
    3. Microscopic examination.

Precautions

  1. Urine must be analyzed within one hour of collection if held at room temperature.
    1. Keep urine at 2 to 8°C if delayed >8 hours.
      1. If urine is kept for a longer time, then it will get a false positive test like nitrite will be positive.
      2. Urea producing organisms will degrade urea to ammonia and change the pH to alkaline.
      3. Change in pH causes degeneration of cast and cell lysis.

Physical Character:

Color

    1. The yellow color of the urine is due to pigment, which is called urochrome and is produced as endogenous metabolism.
    2. Color intensity depends upon the concentration of the urine.
    3. Concentrated urine is darker in color.
    4. The pale yellow to light color is due to diluted urine.
    5. Yellow to amber color is due to urochromes, which are derivatives of urobilin, the end product of bilirubin degradation.
    6. Yellowish-brown to green color is due to bile pigments oxidation.
      1. While the blue/green color is due to pseudomonas infection.
    7. Blue urine color is due to the intake medication of methocarbamol, methylene blue, and amitryptiline.
    8. Red and brown after standing are due to porphyrins.
    9. The reddish-brown color in the fresh sample is from hemoglobin and red blood cells.
      1. When RBCs are there for several hours in acidic urine, it will give rise to brown color due to oxidation of the methemoglobin.
      2. Hemoglobinuria shows red plasma due to hemolysis of the RBCs.
      3. Myoglobin is cleared from the plasma rapidly so that the plasma will be clear.
        Urine blood chemical test positive

        Urine blood chemical test positive

    10. The brownish-black color ion is standing in the urine due to alkaptonuria because of the homogentisic acid excretion. In this case, the chemical blood tests will be negative.
    11. In the case of malignant melanoma where melanogen oxidizes in the air to melanin.
    12. Drugs and some foods like beets may change the urine color.
    13. If urine shows large foam on shaking, it indicates an increased amount of protein in the urine.
      Urine colorEtiology for the color
      Pale yellow to light
      Normal color
      OrangeConcentrated urine
      Pale yellowPolyuria, Diabetes inspidus, and Mellitus
      Deep yellowRiboflavin
      Dark  yellow and dark color
      1. Concentrated urine
      2. Bilirubin
      3. Urobilin
      4. Biliverdin
      Yellow to amber
      1. Urobilin
      2. Bilirubin
      3. Biliverdin
      Amber orangeBilirubin, nitrofurantoin, and pyridium
      Yellow-brown or yellow-greenBilirubin oxidized to biliverdin.
      Yellowish-brown to green
      1. Bile pigments
      2. Bacteria (pseudomonas)
      Red and brown after keeping the urinePorphyrins
      Redish brown in fresh urine
      1. Hemoglobin and red blood cells
      2. Myoglobin
      3. Porphobilinogen
      4. Porphyrins
      Pink to red
      1. RBCs
      2. Hemoglobin
      3. Myoglobin
      4. Beets,
      5. Rifampicin
      6. Menstrual contamination
      Brownish-black colorAlkaptonuria
      Changing colorSome of the drugs
      Green
      1. Pseudomonas infection
      2. Biliverdin
      Green-yellowFlavones in some vitamins
      Green or blueMethylene blue
      Brown-black
      1. RBCs oxidized to methemoglobin.
      2. Melanin
      3. Homogentisic acid
      4. Metronidazole
      5. Methyldopa
      Urine colorPathological causesNonpathological causes
      Red or reddish-brownHemoglobin, RBCs, Myoglobin, porphyrinsDrugs and dye, beets, rhubarb, senna
      GreenBiliverdin, bacteria (pseudomonas)Vitamins, diuretics, psychoactive drugs
      Blue or blue-greenNoneUrinary germicide, diuretics
      OrangeBile pigmentsDrugs like pyridium, phenothiazine
      Yellow-orange or yellow-brownBilirubin, Urobilin, dehydration, feverCarrots, riboflavin, nitrofurantoin
      Black or brownish-blackUrobilin. melanin, methemoglobinIron preparations, levodopa
      Milky or opalescentBacteria and not cleared by acid, fat globules (lipiduria)
Urine colors in various conditions

Urine colors in various conditions

Odor

    1. Odor has little value in the diagnosis of various possibilities.
    2. There is a typical ammonia smell.
      1. When urine is sometimes kept on the table, the odor of ammonia (NH 3) becomes more prominent.
      2. The breakdown of the urea by the bacteria in the urine is responsible for the ammonia smell.
    3. The characteristic pungent odor in fresh urine is due to volatile aromatic acids.
    4. Urinary tract infection gives a noxious, fecal smell, and it is unpleasant to smell.
    5. Diabetic urine often smells fruity as a result of ketones.
    6. Ingestion of onions, garlic, and asparagus can cause an unusual or pungent odor.
    7. Maple syrup odor is seen in maple syrup disease.
    8. A bleach-like smell is seen in contamination.
    9. The mousy odor is seen in phenylketonuria.
      OdorThe reason for that odor
      Faint aromatic (fresh urine)Due to ammonia
      Strong, unpleasant odorBacterial infection
      Sweety or fruity odorDiabetes mellitus ketone bodies
      Maple syrup odorMaple syrup disease
      Unusual pungent odorIngestion of onions, garlic, and asparagus
      Mousy odorPhenylketonuria
      Sweet smellMalnutrition, vomiting, and diarrhea

Clarity

    1. Normal urine is clear and is judged against the light source.
    2. The cloudiness of the urine specimen depends on pH and dissolved solids components like amorphous phosphates and carbonates.
      Urine degree of clarity (cloudiness)
      Criteria
      ClearNo visible particulate material is seen.
      Hazy

      Can see visible particulate material

      Can read the newspaper

      CloudyCan see the newspaper, but the words are distorted or not clear.
      TurbidCan not see the newspaper through the urine tube
    3. Turbidity generally is due to gross bacteriuria.
      1. In alkaline urine, turbidity is due to amorphous phosphates and carbonates.
      2. In acidic urine, turbidity is due to amorphous urates.
    4. Smoky urine is due to hematuria.
    5. In women, the epithelial cells and mucus may result in hazy urine.
    6. Urine, when kept in the fridge, may become turbid without any pathology.
      1. In the refrigerated urine, amorphous phosphates, carbonates, and urates give rise to thick turbidity.
    7. Other turbidity causes are contamination with semen, feces, vaginal cream, talcum powder, and contrast media.
    8. Turbidity may be seen in bacterial infection and the presence of RBCs and WBCs.Common causes of cloudiness in the urine:
      Normally found in the urinePathologic causes
      Amorphous phosphateAmorphous urates
      Amorphous uratesAbnormal crystalluria like cysteine, tyrosine
      Presence of normal crystalsRBCs, WBCs, fat cast
      MucusEpithelial cells like renal transitional cells
      BacteriaBacteria in fresh urine
      SpermatozoaYeast, fungi, and parasites
      Prostatic fluidsFecal material
      Epithelial cells (squamous cells)Chyluria due to lymph is, although rare
      Contamination by powder, antisepticpositive for malignant cells

Specific gravity

    1. The kidneys’ ability to selectively absorb essential chemicals (electrolytes) and water from the glomerular filtrate is one of the most important body functions.
    2. Specific gravity <1.003 is mostly not the urine.
    3. Definition: This is the weight of 1 mL of urine in grams divided by 1 mL of water.
      Urine specific gravity formula

      Urine specific gravity formula

      1. This helps to give the state of hydration and dehydration.
      2. This indicates the concentrating ability of the kidney.
    4. The specific gravity of the urine can be measured by:
      1. Urinometer (hydrometer). This consists of a weighted float attached to the scale that has been calibrated to urine-specific gravity.
        Urine urinometer

        Urine urinometer

      2. Refractometer. This will determine the concentration of the dissolved particles in the urine. This will do by measuring the refractive index. This refractive index compares the velocity of the light in air with the velocity of light in the solution.
        1. The refractometer advantages are that it is needed two or three drops of urine.
          Urine Refractometer

          Urine Refractometer

      3. Chemical reagents strips. These are disposable colorimetric reagent strips. No instrument is needed.
      4. Automated instruments.
    5. Normal: 1.003 to 1.030 (1.005 to 1.030).
      1. Most urine fall in the range of 1.015 to 1.025.
      2. Newborn = 1.012
      3. Infants = 1.002 to 1.006
      4. Adult = 1.002 to 1.030
    6. After 12 hours of fluid restriction = >1.025
    7. Urine 24 hours = 1.015 to 1.025
    8. The diluted urine range is 1.000 to 1.010.
      1. Concentrated urine is 1.025 to 1.030.
    9. Low specific gravity urine (hyposthenuria) is seen in:
      1. Diabetes inspidus (not go above 1.001 to 1.003. ADH hormone is lacking.
      2. Pyelonephritis.
      3. Glomerulonephritis.
      4. The consistent low specific gravity of 1.010 is known as isosthenuria. It is seen in chronic renal disease, where the capacity of concentrating urine is lost.
    10. High specific gravity urine (hypersthenuria) is seen in:
      1. Diabetes mellitus.
      2. Congestive heart failure.
      3. Dehydration due to sweating, fever, and vomiting or diarrhea.
      4. Adrenal insufficiency.
      5. Liver disease.Nephrosis.

pH

    1. Lungs and the kidneys are major regulators of the acid-base balance of the body.
      Urine pH control

      Urine pH control

    2. Urine pH must be performed on a fresh urine sample because the urine tends to change the pH on standing.
    3. The first-morning sample shows a pH of 5 to 6.
      1. After the meal may have alkaline pH.
    4. 4.6 to 7.0 and the average is 6.0
    5. pH depends upon the diet.
    6. pH <7.0 is primarily caused by the phosphates, which are excreted as salts conjugated to Na+, K+, Ca+, and NH4+.
      1. Acidity also reflects the excretion of nonvolatile metabolic acids pyruvate, lactate, and citrate.
    7. The acidity of urine is seen in:
      1. Systemic acidosis in diabetes mellitus.
      2. Renal tubular acidosis.
    8. The alkaline urine (>7.0) is seen in:
      1. This is a normal reaction to the gastric acidity  (HCL) dumped into the duodenum and then to circulation.
      2. Urinary tract infection.
      3. Bacterial contamination of the urine.
      4. Medication like sodium citrate and sodium bicarbonate will reduce pH.
      5. Fanconi’s syndrome is congenital generalized aminoaciduria due to defective proximal tubular dysfunction.
The pH control mechanism in the Urine

The pH control mechanism in the Urine

  1. The Effects of chemical used on urinePossible cause of the turbidity
    Acidic urineAmorphous urates, uric acid, contrast media
    Alkaline  urineAmorphous phosphates, carbonates
    Solubility on heating the urineUric acid crystals and amorphous urates
    Insoluble in dilute acetic acidBacteria, yeast, WBCs, spermatozoa
    Solubility in dilute acetic acidAmorphous phosphate, carbonates, and RBCs
    Solubility in etherLipids, lymph fluid

Osmolality (Osmolarity)

    1. Definition: Specific gravity depends on the number of particles present in a solution and the particles’ density, whereas osmolarity is affected only by the number of particles present.
      1. Osmolarity is the number of solute particles in one liter of the solvent.
      2. Osmolality is the number of solute particles in one Kg of solvent.
      3. The unit of the osmolarity is Osm/L.
      4. The difference in the dilute solution is negligible.
      5. Osmolality is preferred over osmolarity because it is higher.
      6. When evaluating the ability of kidneys concentration, Na+, K+, and Urea are important. All these three contribute to the osmolarity of the urine.
      7. Example: Osmolal solution of the Glucose is 180 g dissolved in 1 Kg of solvent.
          1. The osmolar solution of glucose is 180 g dissolved in 1 Liter of solvent.
          2. The unit used in the laboratory is mOsm (milliosmole).
      8. Use of the osmolality/osmolarity:
        1. It can monitor renal concentration ability for the course of renal disease.
        2. It can monitor fluid and electrolyte therapy.
        3. It can differentiate between hypernatremia and hyponatremia.
        4. It evaluates the secretion and renal response to ADH.
        5. There is a need to get the osmolarity of the serum and the urine.
      9. Normal:
        1. 500 to 800 mOsm/ kg of water.
        2. Serum osmolarity = 275 to 300 mOsm.
        3. Urine osmolarity = 50 to 1400 mOsm.

Volume

    1. The urine volume depends on the amount of water excreted by the kidneys.
    2. The volume of the urine depends upon:
      1. The fluid  (water) intake.
      2. Fluid (water) loss from the nonrenal sources.
      3. The amount of ADH secretion.
      4. Excretion of dissolved solids such as glucose or salts.
    3. The urine volume excreted indicates the balance between fluid ingestion and water loss from the lungs, sweat, and intestine.
    4. Normal:
      1. 1200 to 1500 mL/24 hours.
      2. The range of 600 to 2000 mL/24 hours may be considered normal.
      3. The average urine volume is 1200 ml.
    5. Night urine volume is usually less in amount.
    6. The ratio of day urine to night’s urine is  2: 1 to 4:1.
    7. Nocturnal polyuria:
      1. There is increased urine at night. This may be seen in diabetes mellitus and diabetes inspidus.
      2. This may be seen as diuretics, intake of tea, coffee, or alcohol. These will suppress the ADH.
    8. Polyuria is seen in:
      1. diabetes mellitus.
      2. Diabetes inspidus.
      3. Chronic renal disease.
      4. In the case of acromegaly.
      5. In the case of myxedema.
    9. Oliguria:
      1. There is a decrease in the normal daily urine volume.
        1. Anuria or oliguria, where urine volume is <200 mL/day.
      2. This is seen in dehydration due to vomiting, diarrhea, perspiration, or severe burn.
      3. Nephritis.
      4. Urinary tract obstruction.
      5. Acute renal failure.
      6. Oliguria may lead to anuria.
      7. Drugs that have diuretic effects are:
        1. Thiazides.
        2. Alcohol.
        3. Caffeine.
      8. The drugs which decrease the volume and are nephrotoxic are:
        1. Analgesics like salicylates.
        2. Antibiotics like neomycin, penicillin, and streptomycin.
AgeNormal volume
Newborn
                1 to 2 days30 to 60 mL/24 hours
Infant
              3 to 10 days100 to 300 mL/24 hours
              60 to 365 days400 to 500 mL/24hours
Child
               1 to 3 years500 to 600 mL/24 hours
              8 to 14 years800 o 1400 mL/24 hours
Adult
                 Male800 to 1800 mL/24 hours
                 Female600 to 1600 mL/24 hours
Elderly250 to 2400 mL/24 hours

 

Clinical type of proteinuriaEtiology of proteinuria
Prerenal
  1. I/V hemolysis
  2. Muscle injury
  3. Multiple myeloma
  4. Severe infections
Renal
  1. Immune complex disease
  2. Amyloidosis
  3. Dehydration
  4. Hypertension
  5. Pre-eclampsia
  6. Toxic drugs
  7. Diabetic nephropathy
  8. Strenuous exercise
  9. Orthostatic proteinuria
Postrenal
  1. Lower urinary tract infection
  2. Vaginal secretion
  3. Prostatic fluid /spermatozoa
  4. Menstrual contamination
  5. Injury/trauma
Tubular disorders
  1. Severe viral infections
  2. Toxic injury.
  3. Heavy metal intake
  4. Fanconi’s syndrome
Summary of urine analysis

Summary of urine analysis

Normal urine picture:

Physical featuresChemical featuresMicroscopic findings
  1. Color = Pale yellow or amber
  2. Appearance = Clear to slightly hazy
  3. pH = 4.5 to 8.0
  4. Specific gravity = 1.015 to 1.025
  1. Blood = Negative
  2. Glucose = Negative
  3. Ketones= Negative
  4. Protein = Negative
  5. Bilirubin = Negative
  6. Urobilinogen = Negative (±)
  7. Leucocyte esterase = Negative
  8. Nitrite for bacteria = Negative
  1. RBCs = Rare or Negative
  2. WBC = Rare or Negative
  3. Epithelial cells = Few
  4. Cast = Negative (Occasional hyaline)
  5. Crystal = Negative (Depends upon the pH of the urine)
  6. Bacteria = Negative

Note: Details are seen in Part 3 urine complete analysis.


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Urinalysis

Urinalysis can reveal diseases that have gone unnoticed because they do notproduce striking signs or symptoms. Examples include diabetes mellitus, variousforms of glomerulonephritis, and chronic urinary tract infections.

The most cost-effective device used to screen urine is a paper or plasticdipstick. This microchemistry system has been available for many years andallows qualitative and semi-quantitative analysis within one minute by simplebut careful observation. The color change occurring on each segment of the stripis compared to a color chart to obtain results. However, a careless doctor,nurse, or assistant is entirely capable of misreading or misinterpreting theresults. Microscopic urinalysis requires only a relatively inexpensive lightmicroscope.

MACROSCOPIC URINALYSIS

The first part of a urinalysis is direct visual observation. Normal, freshurine is pale to dark yellow or amber in color and clear. Normal urine volumeis 750 to 2000 ml/24hr.

Turbidity or cloudiness may be caused by excessive cellular material orprotein in the urine or may develop from crystallization or precipitation ofsalts upon standing at room temperature or in the refrigerator. Clearing of thespecimen after addition of a small amount of acid indicates that precipitationof salts is the probable cause of tubidity.

A red or red-brown (abnormal) color could be from a food dye, eating freshbeets, a drug, or the presence of either hemoglobin or myoglobin. If the samplecontained many red blood cells, it would be cloudy as well as red.



Examples of appearances of urine

URINE DIPSTICK CHEMICAL ANALYSIS

Overview

A dipstick is a paper strip with patches impregnated with chemicals that undergo a color change when certain constituents of the urine are present or in a certain concentration. The strip is dipped into the urine sample, and after the appropriate number of seconds, the color change is compared to a standard chart to determine the findings.

(MouseOver [or touch] below for results)

Leukocyte esteraseNitrite pH Protein Blood Specific gravity Ketones GlucoseBilirubin

Findings: Leukocyte esterase 3+, Nitrite Pos; pH 7.0; Protein Neg; Blood Neg; Sp Gr 1.015; Ketones 1+, Glucose 1+; Bilirubin Neg

pH

The glomerular filtrate of blood plasma is usually acidified by renal tubulesand collecting ducts from a pH of 7.4 to about 6 in the final urine. However,depending on the acid-base status, urinary pH may range from as low as 4.5 to ashigh as 8.0. The change to the acid side of 7.4 is accomplished in the distalconvoluted tubule and the collecting duct.

Specific Gravity (sp gr)

Specific gravity of urine is determined by the presence of solutes represented by particles of varying sizes, from small ions to larger proteins. Urine osmolality measures the total number of dissolved particles, regardless of their size. The most common method of measurement is freezing point depression. A refractometer measures the change in direction of a light path (refraction) based upon particle concentration and size in a fluid. Larger particles such as glucose and albumin will alter refraction to a greater degree. The urine dipstick measurement of specific gravity is an approximation that is most sensitive to cationic concentration in urine. Therefore, dipstick specific gravity is altered by very high or low urine pH, but not large particles like proteins.

Urine specific gravity (U-SG) is directly proportional to urine osmolality (U-Osm). A U-Osm of 400 mOsm/Kg equates to sp gr of 1.010, and 800 mOsm/kg to sp gr of 1.020 (Note: the amount of solute in a kilogram of solvent is termed osmolality, and the amount per liter of solvent is osmolarity). The ability of the kidneys to concentrate or dilute the urine over that of plasma is being measured.

Specific gravity between 1.002 and 1.035 on a random sample should beconsidered normal if kidney function is normal. Since the sp gr of theglomerular filtrate in Bowman's space ranges from 1.007 to 1.010, anymeasurement below this range indicates hydration and any measurement above itindicates relative dehydration.

If sp gr is not > 1.022 after a 12 hour period without food or water,renal concentrating ability is impaired and the patient either has generalizedrenal impairment or nephrogenic diabetes insipidus. In end-stage renal disease,sp gr tends to become 1.007 to 1.010.

Any urine having a specific gravity over 1.035 is either contaminated,contains very high levels of glucose, or the patient may have recently receivedhigh density radiopaque dyes intravenously for radiographic studies or low molecular weight dextran solutions. Subtract 0.004 for every 1% glucose to determine non-glucose solute concentration.

Protein

Dipstick screening for protein is done on whole urine, but semi-quantitativetests for urine protein should be performed on the supernatant of centrifugedurine since the cells suspended in normal urine can produce a falsely highestimation of protein. Normally, only small plasma proteins filtered at theglomerulus are reabsorbed by the renal tubule. However, a small amount offiltered plasma proteins and also the uromodulin (Tamm-Horsfall) protein secreted by the tubule cells of the nephron can be found in normal urine. Normal total protein excretion does not usually exceed 150 mg/24 hours or 10 mg/100 mL in any single specimen. More than 150 mg/day is defined as proteinuria. Proteinuria > 3.5 gm/24 hours is severe and known as nephrotic syndrome.

Dipsticks detect protein by production of color with an indicator dye,Bromphenol blue, which is most sensitive to albumin but detects globulins andBence-Jones protein poorly. Precipitation by heat is a better semiquantitativemethod, but overall, it is not a highly sensitive test. The sulfosalicylic acidtest is a more sensitive precipitation test. It can detect albumin, globulins,and Bence-Jones protein at low concentrations.

In rough terms, trace positive results (which represent a slightly hazyappearance in urine) are equivalent to 10 mg/100 ml or about 150 mg/24 hours(the upper limit of normal). 1+ corresponds to about 200-500 mg/24 hours, a 2+to 0.5-1.5 gm/24 hours, a 3+ to 2-5 gm/24 hours, and a 4+ represents 7 gm/24hours or greater.

Glucose

Less than 0.1% of glucose normally filtered by the glomerulus appears inurine (< 130 mg/24 hr). Glycosuria (excess sugar in urine) generally meansdiabetes mellitus. Dipsticks employing the glucose oxidase reaction forscreening are specific for glucos glucose but can miss other reducing sugarssuch as galactose and fructose. For this reason, most newborn and infant urinesare routinely screened for reducing sugars by methods other than glucose oxidase(such as the Clinitest, a modified Benedict's copper reduction test).

Ketones

Ketones (acetone, aceotacetic acid, beta-hydroxybutyric acid) resulting fromeither diabetic ketosis or some other form of calorie deprivation (starvation),are easily detected using either dipsticks or test tablets containing sodiumnitroprusside.

Nitrite

A positive nitrite test indicates that bacteria may be present insignificant numbers in urine. Gram negative rods such as E. coli are morelikely to give a positive test.

Leukocyte Esterase

A positive leukocyte esterase test results from the presence of white bloodcells either as whole cells or as lysed cells. Pyuria can be detected even ifthe urine sample contains damaged or lysed WBC's. A negative leukocyte esterasetest means that an infection is unlikely and that, without additional evidenceof urinary tract infection, microscopic exam and/or urine culture need not bedone to rule out significant bacteriuria.




MICROSCOPIC URINALYSIS

Methodology

A sample of well-mixed urine (usually 10-15 ml) is centrifuged in a testtube at relatively low speed (about 2-3,000 rpm) for 5-10 minutes until amoderately cohesive button is produced at the bottom of the tube. The supernateis decanted and a volume of 0.2 to 0.5 ml is left inside the tube. The sedimentis resuspended in the remaining supernate by flicking the bottom of the tubeseveral times. A drop of resuspended sediment is poured onto a glass slide andcoverslipped.




Examination

The sediment is first examined under low power to identify most crystals,casts, squamous cells, and other large objects. The numbers of casts seen areusually reported as number of each type found per low power field (LPF).Example: 5-10 hyaline casts/L casts/LPF. Since the number of elements found ineach field may vary considerably from one field to another, several fields areaveraged. Next, examination is carried out at high power to identify crystals,cells, and bacteria. The various types of cells are usually described as thenumber of each type found per average high power field (HPF). Example: 1-5WBC/HPF.




Red Blood Cells

Hematuria is the presence of abnormal numbers of red cells in urine due to:glomerular damage, tumors which erode the urinary tract anywhere along itslength, kidney trauma, urinary tract stones, renal infarcts, acute tubularnecrosis, upper and lower uri urinary tract infections, nephrotoxins, andphysical stress. Red cells may also contaminate the urine from the vagina inmenstruating women or from trauma produced by bladder catherization. Theoretically, no red cells should be found, but some find their way into theurine even in very healthy individuals. However, if one or more red cells canbe found in every high power field, and if contamination can be ruled out, thespecimen is probably abnormal.

RBC's may appear normally shaped, swollen by dilute urine (in fact, onlycell ghosts and free hemoglobin may remain), or crenated by concentrated urine. Both swollen, partly hemolyzed RBC's and crenated RBC's are sometimes difficultto distinguish from WBC's in the urine. In addition, red cell ghosts maysimulate yeast. The presence of dysmorphic RBC's in urine suggests a glomerular disease such as a glomerulonephritis. Dysmorphic RBC's have odd shapes as a consequence of being distorted via passage through the abnormal glomerular structure.



Red blood cells in urine

Dysmorphic red blood cells in urine




White Blood Cells

Pyuria refers to the presence of abnormal numbers of leukocytes that mayappear with infection in either the upper or lower urinary tract or with acuteglomerulonephritis. Usually, the WBC's are granulocytes. White cells from thevagina, especially in the presence of vaginal and cervical infections, or theexternal urethral meatus in men and women may contaminate the urine.

If two or more leukocytes per each high power field appear in non-contaminated urine, the specimen is probably abnormal. Leukocytes have lobed nuclei and granular cytoplasm.



White blood cells in urine


Epithelial Cells

Renal tubular epithelial cells, usually larger than granulocytes, contain alarge round or oval nucleus and normally slough into the urine in small numbers. However, with nephrotic syndrome and in conditions leading to tubulardegeneration, the number sloughed is increased.

When lipiduria occurs, these cells contain endogenous fats. When filled with numerous fat droplets, such cells are called oval fat bodies. Oval fat bodies exhibit a "Maltese cross" configuration by polarized light microscopy.



Oval fat bodies in urine

Oval fat bodies in urine, with polarized light

Transitional epithelial cells from the renal pelvis, ureter, or bladder havemore regular cell borders, larger nuclei, and smaller overall size than squamousepithelium. Renal tubular epithelial cells are smaller and rounder thantransitional epithelium, and their nucleus occupies more of the total cellvolume.

Squamous epithelial cells from the skin surface or from the outer urethra can appear in urine.

Their significance is that they represent possible contamination of the specimen with skin flora.



Squamous epithelial cells in urine


Casts

Urinary casts are formed only in the distal convoluted tubule (DCT) or thecollecting duct (distal nephron). The proximal convoluted tubule (PCT) and loop of Henle are not locations for cast formation. Hyaline casts are composed primarily of a mucoprotein (Tamm-Horsfall protein) secreted by tubule cells. The Tamm-Horsfall protein secretion (green dots) is illustrated in the diagram below, forming a hyaline cast in the collecting duct:

Even with glomerular injury causing increased glomerular permeability to plasma proteins with resulting proteinuria, most matrix or "glue" that cements urinary casts together is Tamm-Horsfall mucoprotein, although albumin and some globulins are also incorporated. An example of glomerular inflammation with leakage of RBC's to produce a red blood cell cast is shown in the diagram below:

The factors which favor protein cast formation are low flow rate, high saltconcentration, and low pH, all of which favor protein denaturation andprecipitation, particularly that of the Tamm-Horsfall protein. Protein castswith long, thin tails formed at the junction of Henle's loop and the distalconvoluted tubule are called cylindroids. Hyaline casts can be seen even inhealthy patients.

Red blood cells may stick together and form red blood cell casts. Such casts are indicative of glomerulonephritis, with leakage of RBC's from glomeruli, or severe tubular damage.

White blood cell casts are most typical for acute pyelonephritis, but they may also be present with glomerulonephritis. Their presence indicates inflammation of the kidney, because such casts will not form except in the kidney.

When cellular casts remain in the nephron for some time before they areflushed into the bladder urine, the cells may degenerate to become a coarselygranular cast, later a finely granular cast, and ultimately, a waxy cast. Granular and waxy casts are be believed to derive from renal tubular cell casts.Broad casts are believed to emanate from damaged and dilated tubules and aretherefore seen in end-stage chronic renal disease.


The so-called telescoped urinary sediment is one in which red cells, whitecells, oval fat bodies, and all types of casts are found in more or less equalprofusion. The conditions which may lead to a telescoped sediment are: 1) lupusnephritis 2) hypertensive emergency 3) diabetic glomerulosclerosis, and4) rapidly progressive glomerulonephritis.

In end-stage kidney disease of any cause, the urinary sediment often becomesvery scant because few remaining nephrons produce dilute urine.



Hyaline casts in urine

Red blood cell casts forming in tubules

Red blood cell cast in urine

White blood cell cast in urine

Renal tubular cell cast in urine

Granular casts in urine

Granular cast in urine

Waxy cast in urine

Bile stained hyaline casts in renal tubules




Bacteria

Bacteria are common in urine specimens because of the abundant normalmicrobial flora of the vagina or external urethral meatus and because of theirability to rapidly multiply in urine standing at room temperature. Therefore,microbial organisms found in all but the most scrupulously collected urinesshould be interpreted in view of clinical symptoms.

Diagnosis of bacteriuria in a case of suspected urinary tract infectionrequires culture. A colony count may also be done to see if significant numbersof bacteria are present. Generally, more than 100,000/ml of one organismreflects significant bacteriuria. Multiple organisms reflect contamination. However, the presence of any organism in catheterized or suprapubic tapspecimens should be considered significant.




Yeast

Yeast cells may be contaminants or represent a true yeast infection. Theyare often difficult to distinguish from red cells and amorphous crystals but aredistinguished by their tendency to bud. Most often they are Candida, which maycolonize bladder, urethra, or vagina.




Crystals

Common crystals seen even in healthy patients include calcium oxalate,triple phosphate crystals and amorphous phosphates.

Very uncommon crystals include: cystine crystals in urine of neonates withcongenital cystinuria or severe liver disease, tyrosine crystals with congenitaltyrosinosis or marked liver impairment, or leucine crystals in patients withsevere liver disease or with maple syrup urine disease.



Oxalate crystals in urine

Triple phosphate crystals in urine

Cystine crystals in urine




Miscellaneous

General "crud" or unidentifiable objects may find their way into a specimen, particularly those that patients bring from home.

Spermatozoa can sometimes be seen. Rarely, pinworm ova may contaminate theurine. In Egypt, ova from bladder infestations with schistosomiasis may be seen.




METHODS OF URINE COLLECTION

  1. Random collection taken at any time of day with no precautions regardingcontamination. The sample may be dilute, isotonic, or hypertonic and maycontain white cells, bacteria, and squamous epithelium as contaminants. Infemales, the specimen may cont contain vaginal contaminants such astrichomonads, yeast, and during menses, red cells.

  2. Early morning collection of the sample before ingestion of any fluid. This is usually hypertonic and reflects the ability of the kidney to concentrateurine during dehydration which occurs overnight. If all fluid ingestion hasbeen avoided since 6 p.m. the previous day, the specific gravity usually exceeds1.022 in healthy individuals.

  3. Clean-catch, midstream urine specimen collected after cleansing theexternal urethral meatus. A cotton sponge soaked with benzalkoniumhydrochloride is useful and non-irritating for this purpose. A midstream urineis one in which the first half of the bladder urine is discarded and thecollection vessel is introduced into the urinary stream to catch the last half. The first half of the stream serves to flush contaminating cells and microbesfrom the outer urethra prior to collection. This sounds easy, but it isn't (tryit yourself before criticizing the patient).

  4. Catherization of the bladder through the urethra for urine collection iscarried out only in special circumstances, i.e., in a comatose or confusedpatient. This procedure risks introducing infection and traumatizing theurethra and bladder, thus producing iatrogenic infection or hematuria.

  5. Suprapubic transabdominal needle aspiration of the bladder. When doneunder ideal conditions, this provides the purest sampling of bladder urine. This is a good method for infants and small children.

Summary

To summarize, a properly collected clean-catch, midstream urine aftercleansing of the urethral meatus is adequate for complete urinalysis. In fact,these specimens generally suffice even for urine culture. A period ofdehydration may precede urine collection if testing of renal concentration isdesired, but any specific gravity > 1.022 measured in a randomly collectedspecimen denotes adequate renal concentration so long as there are no abnormalsolutes in the urine.

Another important factor is the interval of time which elapses fromcollection to examination in the laboratory. Changes which occur with timeafter collection include: 1) decreased clarity due to crystallization ofsolutes, 2) rising pH, 3) loss of ketone bodies, 4) loss of bilirubin, 5)dissolution of cells and casts, and 6) overgrowth of contaminatingmicroorganisms. Generally, urinalysis may not reflect the findings of absolutely fresh urine if the sample is > 1 hour old. Therefore, get theurine to the laboratory as quickly as possible.

Sours: https://webpath.med.utah.edu/TUTORIAL/URINE/URINE.html
Interpretation of the Urinalysis (Part 3) - Microscopy and Summary

24.4A: Physical Characteristics of Urine

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Urine is a sterile waste product composed of water soluble nitrogen products.

Learning Objectives

  • List the physical characteristics of urine

Key Points

  • Urine color is an indicator for hydration.
  • Urine pH is often influenced by diet.
  • Urine smell indicates age of the urine and may indicate the prescence of glucose and ketones.
  • Urine turbidity may indicate urinary tract infection or obstruction.
  • Urinalysis is the process of analyzing and detecting chemicals excreted in urine.
  • Physical characteristics of urine include color, smell, pH, density and turbidity

Key Terms

  • urine: A liquid excrement consisting of water, salts, and urea, which is made in the kidneys then released through the urethra.
  • urinalysis: A urinalysis (UA), also known as Routine and Microscopy (R&M), is an array of tests performed on urine, and one of the most common methods of medical diagnosis.

Urine, a typically sterile liquid by-product of the body, is secreted by the kidneys through a process called urination and excreted through the urethra. Urine is often used as a diagnostic feature for many disease conditions. These may b based on either physical or chemical components, that may give insight to processes within the body, often through urinalysis, a common clinical analysis of urine.

Physical Characteristics

Physical characteristics that can be applied to urine include color, turbidity (transparency), smell (odor), pH (acidity – alkalinity) and density. Many of these characteristics are notable and identifiable by by vision alone, but some require laboratory testing.

  • Color: Typically yellow-amber, but varies according to recent diet and the concentration of the urine. Drinking more water generally tends to reduce the concentration of urine, and therefore causes it to have a lighter color. Dark urine may indicate dehydration. Red urine indicates red blood cells within the urine, a sign of kidney damage and disease.
  • Smell: The smell of urine may provide health information. For example, urine of diabetics may have a sweet or fruity odor due to the presence of ketones (organic molecules of a particular structure) or glucose. Generally fresh urine has a mild smell but aged urine has a stronger odor similar to that of ammonia.
  • The pH of normal urine is generally in the range 4.6 – 8, with a typical average being around 6.0. Much of the variation occurs due to diet. For example, high protein diets result in more acidic urine, but vegetarian diets generally result in more alkaline urine (both within the typical range of 4.6 – 8).
  • Density: Density is also known as “specific gravity.” This is the ratio of the weight of a volume of a substance compared with the weight of the same volume of distilled water. The density of normal urine ranges from 0.001 to 0.035.
  • Turbidity: The turbidity of the urine sample is gauged subjectively and reported as clear, slightly cloudy, cloudy, opaque or flocculent. Normally, fresh urine is either clear or very slightly cloudy. Excess turbidity results from the presence of suspended particles in the urine, the cause of which can usually be determined by the results of the microscopic urine sediment examination. Common causes of abnormal turbidity include: increased cells, urinary tract infections or obstructions.

Abnormalities in any of these of physical characteristics may indicate disease or metabolic imbalances. These problems may seem superficial or minor on their own, but can actually be the symptoms for more serious diseases, such as diabetes mellitus, or a damaged glomerulus.

Sours: https://med.libretexts.org/Bookshelves/Anatomy_and_Physiology/Book%3A_Anatomy_and_Physiology_(Boundless)/24%3A__Urinary_System/24.4%3A_Urine/24.4A%3A_Physical_Characteristics_of_Urine

Chart urine turbidity

Physical Characteristics of Urine

Urine is a sterile waste product composed of water soluble nitrogen products.

Learning Objectives

List the physical characteristics of urine

Key Takeaways

Key Points

  • Urine color is an indicator for hydration.
  • Urine pH is often influenced by diet.
  • Urine smell indicates age of the urine and may indicate the prescence of glucose and ketones.
  • Urine turbidity may indicate urinary tract infection or obstruction.
  • Urinalysis is the process of analyzing and detecting chemicals excreted in urine.
  • Physical characteristics of urine include color, smell, pH, density and turbidity

Key Terms

  • urine: A liquid excrement consisting of water, salts, and urea, which is made in the kidneys then released through the urethra.
  • urinalysis: A urinalysis (UA), also known as Routine and Microscopy (R&M), is an array of tests performed on urine, and one of the most common methods of medical diagnosis.

Urine, a typically sterile liquid by-product of the body, is secreted by the kidneys through a process called urination and excreted through the urethra. Urine is often used as a diagnostic feature for many disease conditions. These may b based on either physical or chemical components, that may give insight to processes within the body, often through urinalysis, a common clinical analysis of urine.

Physical Characteristics

Physical characteristics that can be applied to urine include color, turbidity (transparency), smell (odor), pH (acidity – alkalinity) and density. Many of these characteristics are notable and identifiable by by vision alone, but some require laboratory testing.

  • Color: Typically yellow-amber, but varies according to recent diet and the concentration of the urine. Drinking more water generally tends to reduce the concentration of urine, and therefore causes it to have a lighter color. Dark urine may indicate dehydration. Red urine indicates red blood cells within the urine, a sign of kidney damage and disease.
  • Smell: The smell of urine may provide health information. For example, urine of diabetics may have a sweet or fruity odor due to the presence of ketones (organic molecules of a particular structure) or glucose. Generally fresh urine has a mild smell but aged urine has a stronger odor similar to that of ammonia.
  • The pH of normal urine is generally in the range 4.6 – 8, with a typical average being around 6.0. Much of the variation occurs due to diet. For example, high protein diets result in more acidic urine, but vegetarian diets generally result in more alkaline urine (both within the typical range of 4.6 – 8).
  • Density: Density is also known as “specific gravity.” This is the ratio of the weight of a volume of a substance compared with the weight of the same volume of distilled water. The density of normal urine ranges from 0.001 to 0.035.
  • Turbidity: The turbidity of the urine sample is gauged subjectively and reported as clear, slightly cloudy, cloudy, opaque or flocculent. Normally, fresh urine is either clear or very slightly cloudy. Excess turbidity results from the presence of suspended particles in the urine, the cause of which can usually be determined by the results of the microscopic urine sediment examination. Common causes of abnormal turbidity include: increased cells, urinary tract infections or obstructions.

Abnormalities in any of these of physical characteristics may indicate disease or metabolic imbalances. These problems may seem superficial or minor on their own, but can actually be the symptoms for more serious diseases, such as diabetes mellitus, or a damaged glomerulus.

Chemical Composition of Urine

Normal urine consists of water, urea, salts, and pigments.

Learning Objectives

Describe how normal urine consists of water, urea, salts and pigment

Key Takeaways

Key Points

  • Urine is a liquid by-product of the body secreted by the kidneys through a process called urination and excreted through the urethra.
  • Urine is an aqueous solution of greater than 95% water. Other constituents include urea, chloride, sodium, potassium, creatinine and other dissolved ions, and inorganic and organic compounds.
  • Urea is a non-toxic molecule made of toxic ammonia and carbon dioxide. Any abnormal constituents found in urine are an indication of disease.
  • The presence of red blood cells in urine is referred to as haematuria.
  • The presence of proteins, which are normally too large to pass through the tubules, can be an indication of damage to the tubules, and is called proteinuria.

Key Terms

  • urine: A liquid excrement that consists of water, salts, and urea, and is made in the kidneys then released through the urethra.
  • diabetes: A group of endocrine diseases whereby a person has high blood sugar due to an inability to produce, metabolize, or respond to the hormone insulin.

Urine is a liquid byproduct of the body secreted by the kidneys through a process called urination and excreted through the urethra. The normal chemical composition of urine is mainly water content, but it also includes nitrogenous molecules, such as urea, as well as creatinine and other metabolic waste components. 

Other substances may be excreted in urine due to injury or infection of the glomeruli of the kidneys, which can alter the ability of the nephron to reabsorb or filter the different components of blood plasma.

Normal Chemical Composition of Urine

Urine is an aqueous solution of greater than 95% water, with a minimum of these remaining constituents, in order of decreasing concentration:

  • Urea 9.3 g/L.
  • Chloride 1.87 g/L.
  • Sodium 1.17 g/L.
  • Potassium 0.750 g/L.
  • Creatinine 0.670 g/L.
  • Other dissolved ions, inorganic and organic compounds (proteins, hormones, metabolites). 

Urine is sterile until it reaches the urethra, where epithelial cells lining the urethra are colonized by facultatively anaerobic gram-negative rods and cocci. Urea is essentially a processed form of ammonia that is non-toxic to mammals, unlike ammonia, which can be highly toxic. It is processed from ammonia and carbon dioxide in the liver.

Abnormal Types of Urine

There are several conditions that can cause abnormal components to be excreted in urine or present as abnormal characteristics of urine. They are mostly referred to by the suffix -uria. Some of the more common types of abnormal urine include:

  • Proteinuria—Protein content in urine, often due to leaky or damaged glomeruli.
  • Oliguria—An abnormally small amount of urine, often due to shock or kidney damage.
  • Polyuria—An abnormally large amount of urine, often caused by diabetes.
  • Dysuria—Painful or uncomfortable urination, often from urinary tract infections.
  • Hematuria—Red blood cells in urine, from infection or injury.
  • Glycosuria— Glucose in urine, due to excess plasma glucose in diabetes, beyond the amount able to be reabsorbed in the proximal convoluted tubule.

Regulation of Urine Concentration and Volume

Antidiuretic hormone (ADH) is produced by the pituitary gland to control the amount of water that is reabsorbed through the collecting ducts.

Learning Objectives

Describe how regulating the amount of water excreted in urine is an essential component of homeostasis that is regulated by the antidiuretic hormone (ADH)

Key Takeaways

Key Points

  • Urine volume and concentration is regulated through the same processes that regulate blood volume.
  • Antidiuretic hormone (ADH)—produced by the posterior pituitary gland —increases the amount of water reabsorbed in the distal convoluted tubule and collecting duct.
  • Osmoreceptors in the hypothalamus signal the posterior pituitary gland to increase ADH secretion when plasma osmolarity becomes too high.
  • ADH causes decreased urine volume and decreased plasma osmolarity.
  • A diuretic increases urine volume and increases plasma osmolarity.
  • Common diuretics include alcohol, water, caffeine, and many medications, and they generally function as diuretics via different mechanisms.

Key Terms

  • diuretic: A substance that increases urine volume and increases plasma osmolarity, often by inhibiting ADH secretion to prevent water reabsorption in the nephron.
  • antidiuretic hormone: A hormone secreted by the posterior pituitary gland that increases water retention to decrease urine volume and decrease plasma osmolarity.

Urine is produced not only to eliminate many cellular waste products, but also to control the amount of water in the body. In a way, urine volume regulation is part of homeostasis, in that it directly regulates blood volume, because greater amounts of urine will reduce the volume of waters in blood. 

There are a few complex systems involved in regulating blood volume and urine production, such as the intricate renin–angiotensin system, and the simpler anti-diuretic hormone (ADH) feedback system.

Anti-Diuretic Hormone Feedback

An anti-diruetic is a substance that decreases urine volume, and ADH is the primary example of it within the body. ADH is a hormone secreted from the posterior pituitary gland in response to increased plasma osmolarity (i.e., increased ion concentration in the blood), which is generally due to an increased concentration of ions relative to the volume of plasma, or decreased plasma volume. 

The increased plasma osmolarity is sensed by osmoreceptors in the hypothalamus, which will stimulate the posterior pituitary gland to release ADH. ADH will then act on the nephrons of the kidneys to cause a decrease in plasma osmolarity and an increase in urine osmolarity.

ADH increases the permeability to water of the distal convoluted tubule and collecting duct, which are normally impermeable to water. This effect causes increased water reabsorption and retention and decreases the volume of urine produced relative to its ion content. 

After ADH acts on the nephron to decrease plasma osmolarity (and leads to increased blood volume) and increase urine osmolarity, the osmoreceptors in the hypothalamus will inactivate, and ADH secretion will end. Due to this response, ADH secretion is considered to be a form of negative feedback.

Diuretics

A diuretic is any substance that has the opposite effect of ADH— they increase urine volume, decrease urine osmolarity, lead to an increased plasma osmolarity, and often reduced blood volume. Many substances can act as diuretics, albeit with different mechanisms. 

A common example is alcohol and water ingestion, which directly inhibit ADH secretion in the pituitary gland. Alternatively caffeine is a diuretic because it interferes with sodium reabsorption (reducing the amount of water reabsorbed by sodium cotransport) and increases the glomerular filtration rate by temporarily increasing blood pressure. Many medications are diuretics because they inhibit the ATPase pumps, thus slowing water reabsorption further.

This is a diagram of the process of urine formation. As the fluid flows along the proximal convoluted tubule useful substances like glucose, water, salts, potassium ions, calcium ions, and amino acids are reabsorbed into the blood capillaries that form a network around the tubules. Many of these substances are transported by active transport and energy is required.

Summary of the process of urine formation: As the fluid flows along the proximal convoluted tubule useful substances like glucose, water, salts, potassium ions, calcium ions, and amino acids are reabsorbed into the blood capillaries that form a network around the tubules. Many of these substances are transported by active transport and energy is required.

Urinalysis

Urinalysis is the process of analyzing urine for target parameters of health and disease.

Learning Objectives

Describe how urinalysis can be used as a method of diagnosis in medicine

Key Takeaways

Key Points

  • The characteristics that can be detected in urine include cells, substances, and properties, such as specific gravity or pH.
  • Urinalysis can be performed on test strips (routine) by light microscopy.
  • The numbers and types of cells and/or material, such as urinary casts, can yield a great detail of information and may suggest a specific diagnosis.
  • Urinary casts include hyaline casts, granular casts, white blood cell casts, red blood cell casts, epithelial cell casts, or bacterial cell casts, which all indicate different abnormalities within urine.

Key Terms

  • urinary cast: Tiny structures formed from bound abnormal cells and molecules within the nephrons that are excreted in urine.
  • urinalysis: Also known as routine and microscopy (R&M), this is an array of tests performed on urine, and one of the most common methods of medical diagnosis.

Urinalysis

A urinalysis (UA), also known as routine and microscopy (R&M), is an array of tests performed on urine, and one of the most common methods of medical diagnosis. Urinalysis means the analysis of urine, and it is used to diagnose several diseases. 

The target parameters that are measured or quantified in urinalysis include many substances and cells, as well as other properties, such as specific gravity. A part of a urinalysis can be performed by using urine test strips, in which the test results can be read as the strip’s color changes. Another method is light microscopy of urine samples. 

When doctors order a urinalysis, they will request either a routine urinalysis or a routine and microscopy (R&M) urinalysis; the difference being that a routine urinalysis does not include microscopy or culture. R&M is used specifically for culturing bacteria found in urine, which can make it an important tool for diagnosing specific urinary tract infections.

Test Strip Urinalysis

Test strip urinalysis exposes urine to strips that react if the urine contains certain cells or molecules. Test strip urinalysis is the most common technique used in routine urinalysis. A urine test strip can identify:

  • Leukocytes—their presence in urine is known as leukocyturia.
  • Nitrites—their presence in urine is known as nitrituria.
  • Proteins —their presence in urine is known as proteinuria, albuminuria, or microalbuminuria.
  • Blood—its presence in urine is known as hematuria.
  • pH—the acidity of urine is easily quantified by test strips, which can identify cases of metabolic acidosis or alkalosis.

Urine Microscopy

The numbers and types of cells and/or material, such as urinary casts, can yield a great detail of information and may suggest a specific diagnosis. A urinary cast is any tiny structure found in urine that consists of multiple molecules or cells bound together. 

Casts form within the nephron when abnormal cells and molecules are filtered from blood, and are excreted as the bound structures in urine. Microscopy can identify casts in urine and use them to diagnose kidney diseases, by characterizing symptoms such as: 

  • Red blood cell casts are associated with glomerulonephritis, vasculitis, or malignant hypertension.
  • White blood cell casts are associated with acute interstitial nephritis, exudative glomerulonephritis, or severe pyelonephritis.
  • Epithelial cell casts are associated with toxin-induced, acute tubular necrosis, hepatitis, and cytomegalovirus.
  • (Heme) granular casts are associated with acute tubular necrosis, and are often composed of proteins, especially antibodies.
  • Hyaline casts are associated with dehydration; it is the most common type of cast.
  • Bacterial casts are associated with urinary tract infection; the cast may be cultured in order to identify the causative organism of the cast.
This is a photo about urinalysis. The photo shows white blood cells as seen under a microscope from a urine sample.

Urinalysis: White blood cells seen under a microscope from a urine sample.

Renal Clearance

Clearance is a measurement of the renal excretion ability.

Learning Objectives

Describe how clearance is a measure of the renal excretion ability

Key Takeaways

Key Points

  • Each substance has a specific clearance that depends on its filtration characteristics, size, and molecular structure.
  • Clearance is dependent upon glomerular filtration, secretion, and reabsorption.
  • Clearance may be either constant or variable over time.
  • Many drugs can either be bound to plasma proteins or unbound in plasma; however, they will not be cleared from the body when bound to proteins.
  • Renal clearance is the main form of clearance in the body, and when combined with other routes of clearance in the body it accounts for most of the total body clearance.

Key Terms

  • nephron: The basic structural and functional unit of the kidney that filters the blood in order to regulate chemical concentrations and thereby produce urine.
  • Renal clearance: The rate at which a substance is removed from the plasma via renal system activity over a unit of time.

Clearance

In renal physiology, clearance is a measurement of the renal excretion ability, which measures the amount of plasma from which a substance is removed from the body over an interval of time. Each substance has its own specific clearance that depends on its unique filtration characteristics. 

Clearance is a function of glomerular filtration, secretion from the peritubular capillaries to the nephron, and reabsorption from the nephron back to the peritubular capillaries. Clearance can be either a constant or variable component over time, depending on the type of substance.

This diagram shows the basic physiologic mechanisms of the kidney; namely, filtration, reabsorption, secretion, and excretion.

Physiology of the nephron: Diagram showing the basic physiologic mechanisms of the kidney.

Clearance Mechanisms

Renal clearance depends mainly on GFR, tubular absorption, and tubular secretion. If any of those variables change, the renal clearance rate of a substance will change as well. These variables alter clearance through the following rules:

  • Increased GFR will increase clearance, while decreased GFR will decrease clearance.
  • Increased tubular secretion will increase clearance, while decreased tubular secretion will decrease clearance. This variable is sometimes altered through changes in the expression of ATPase pumps involved in active transport.
  • Increased tubular reabsorption will decrease clearance, while increased tubular reabsorption will increase clearance.

Additionally, the characteristics of the substance of interest will also determine some components of clearance. For example, certain pharmaceuticals have the tendency to bind to plasma proteins or exist unbound in plasma. Only those that are unbound will be filtered and cleared from the body. Size and molecular structure will also alter the clearance rate.

It is also important to note that renal clearance is not the only form of clearance that occurs for the substances within the plasma of the body. The other types of clearance are 

  • Biliary (through bile). 
  • Salivary.
  • Pulmonary clearance (removed during alveolar gas exchange).

These types of clearance may also excrete certain molecules from the bloodstream based on their size and molecular structure; however, these forms of clearance are generally relatively minor compared to renal clearance. 

These types of clearance all add up to a summation known as total body clearance, which refers to the removal of a substance from the plasma over time, incorporating all routes of removal in the body.

Sours: https://courses.lumenlearning.com/boundless-ap/chapter/urine/
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