Urinalysis & Body Fluids Review Flashcards
What is the functional unit of the kidney? What does it consist of?
The nephron: consists of the glomerulus, Bowman’s capsule, the proximal convoluted tubule, the Loop of Henle, and the distal convoluted tubule.
What are the 3 renal functions associated with urine formation?
(1) filtration - takes place in the glomeruli
(2) reabsorption - renal tubules
(3) secretion - renal tubules
During urine formation, which substances are NOT allowed to filter through the glomerulus in significant amounts?
Protein and cells
Where does water reabsorption take place in the nephron?
Proximal and Distal tubules
Where does reabsorption of glucose take place in the nephron?
Proximal tubules
Which hormone controls reabsorption of water in the distal tubules?
Anti-diuretic hormone (ADH) - produced in the hypothalamus and stores/secreted by the posterior pituitary.
Which hormone controls reabsorption of sodium?
Aldosterone - produced in adrenal cortex
Reabsorption of sodium is linked to excretion of K+ and H+.
What are the main constituents of urine?
Water, urea, sodium, and chloride
Urea (breakdown product of protein) accounts for about 1/2 of the dissolved solute in urine.
What tests could be done on an unknown fluid to determine if it is urine?
Urea, creatine, sodium, and chloride.
Urine has a higher concentration of these substances than other body fluids.
What is osmolality?
The measurement of the number of solute particles per unit of solvent, irrespective of molecular weight.
How is osmolality measured in most clinical laboratories?
Freezing point depression
(Each mOsm of solute lowers the freezing point of urine by 0.00186*C.)
What quality control is required for osmometers?
Osmometers should be checked each day of use with controls of known osmolality.
Why is osmolality a better measurement of kidney function than specific gravity?
It is a better reflection of the concentrating ability of the kidneys since it is not disproportionately affected by the presence of high-molecular-weight substances like glucose and protein.
What is normal urine osmolality?
50-1400 mOsm/Kg depending on factors such as diet and exercise
In a healthy person with a regular diet and fluid intake: 500-850 mOsm/Kg.
What is the normal ratio of urine to plasma osmolality?
Under random conditions: at least 1:1
After controlled fluid intake: 3:1
What is widely accepted as the best overall measure of kidney function?
Glomerular filtration rate (GFR)
(A decrease in GFR precedes kidney failure.)
What test is commonly performed to estimate the glomerular filtration rate?
Creatinine clearance - measures the rate at which the kidneys are able to remove creatinine from the blood.
Creatinine is a good substance to use for a clearance because it is not significantly reabsorbed by the renal tubules, and since it is related to muscle mass, its concentration is constant.
Decreased levels are an indication of impaired renal function..
It does NOT detect early renal disease.
What is the formula for calculating creatinine clearance?
UV/P x 1.73/A
U = urine creatinine in mg/dL
V = urine volume in mL/minute (24 hr volume/1440)
P = plasma creatinine in mg/dL
A = patient’s body surface area (determined by height and weight and obtained from a nomogram)
What is the reference range for creatinine clearance?
Males: 97-137 mL/minute
Females: 88-128 mL/minute
Creatinine clearance decreases with age by about 6.5 mL per minute per decade.
What is the greatest source of error in the creatinine clearance?
Over- or under-collection of the specimen by the patient due to not understanding the collection procedure.
The test requires an accurate 24-hr collection.
The patient must be instructed to discard the urine voided at a specific time on Day 1 (e.g., 7 AM) and to collect the remainder of the voids that day and night, as well as the void at teh same specific time on Day 2 (e.g., 7 AM).
What is recommended as a more accurate assessment of GFR?
The National Kidney Disease Education Program recommends calculating GFR using the Modification of Diet in Renal Disease equation, which factors in serum creatinine, BUN, albumin, age, gender, and race. The NKDEP encourages reporting of the estimated GFR along with the serum creatinine result. The value can be calculated by the chemistry analyzer.
Calculate the creatinine clearance from the data below:
Urine creatinine: 127 mg/dL
Plasma creatinine: 1.4 mg/dL
24 hour urine volume: 1.5 L
Patient surface area: 1.5 m2
[(127 x (1500/1400) / (1.4)] x (1.73/1.5) = 109 mL/min
What is the preferred specimen for routine urinanalysis?
first morning specimen
*it is more concentrated
*it has the lowest pH of the day, so formed elements are preserved better
(Dilute random urines may result in false-negative results for chemical and/or microscopic analysis.)
Ideally, how soon after collection should a urine specimen be tested?
Within 1-2 hours, otherwise it should be refrigerated or chemically preserved.
What is the preferred method of preservation of urine for routine urinalysis?
Refrigeration for up to 6-8 hours
(This slows the multiplication of bacteria, but does not prevent the lytic effect of low specific gravity or alkaline pH. Refrigeration may induce crystal formation, which can obscure other elements in the urine sediment. Warming the specimen to 37*C prior to centrifugation may dissolve these crystals.)
What changes occur in a urine specimen at room temperature?
pH increases - bacteria break down urea to ammonia
glucose decreases - metabolism by bacteria and cells
Ketones, bilirubin, and urobilinogen are lost
Cells & casts lyse
What is the clinical significance of specific gravity?
It is a measurement of the dissolved solute in the urine and reflects the concentrating ability of the kidneys.
Which substances contribute most to specific gravity of a normal urine?
Urea and sodium chloride
What is the normal specific gravity of a random urine?
1.001 to 1.035
What is the normal specific gravity of a 24 hour specimen?
1.015 to 1.025
What is hyposthenuria and what is its significance?
Urine specific gravity less than 1.010.
It indicates that the kidneys have lost their concentrating ability.
What is isothenuria and what is its significance?
Urine specific gravity fixed at 1.010.
This is the specific gravity of the plasma filtrate and indicates that the kidneys can neither concentrate nor dilute the urine.
How is urine specific gravity affected by diabetes mellitus?
It is INCREASED due to the presence of GLUCOSE.
(Glucose molecules have a large effect on specific gravity because of their molecular weight. In this case, the specific gravity is NOT a true reflection of the kidney’s concentrating ability, and the specific gravity should be corrected.)
DM = increased SG but decreased urine volume
A urine with a specific gravity reading of 1.035 by refractometer contains 1 g/dL of glucose and 1 g/dL of protein. What is the corrected specific gravity?
1.028
For each gram/dL of glucose, 0.004 is subtracted.
For each gram/dL of protein, 0.003 is subtracted.
How is specific gravity affected by diabetes insipidus?
It is DECREASED.
(A deficiency of ADH decreases the amount of water reabsorbed, so the urine is dilute. Specific gravity with DI is usually around 1.001-1.003.)
How is the accuracy of the refractometer checked?
It is checked daily with distilled water (1.000) and commercial controls or solutions of known specific gravity, such as 5% NaCl (1.022).
The specific gravity of distilled water reads 1.004 on a refractometer. What should be done before testing specimens?
The set screw of the refractometer should be adjusted to give a reading of 1.000.
A urine specific gravity is off the scale of the refractometer. The technologist dilutes the urine 1:2 and reads the result as 1.020. What value should be reported?
1.040
(The last 2 digits must be multiplied by the reciprocal of teh dilution [2]. Some laboratories would report the specific gravity as “greater than 1.035” and not do a dilution.)
What is another name for a refractometer?
T.S. meter (total solid meter)
How does the refractometer measure specific gravity?
By refractive index, a comparison of the velocity of light in air with the velocity of light in a solution.
Urine is removed from the refrigerator and tested for specific gravity by refractometer. What correction is required for temperature?
None.
(The refractometer is temperature compensated.)
A urine has a specific gravity of 1.040 by refractometer. what might be the cause of the high specific gravity?
Since a specific gravity of 1.040 is physiologically impossible, it indicates the presence of an iatrogenic (medically administered) high-molecular-weight solute, such as radiopaque dyes (radiographic contrast media, x-ray dye).
Although large quantities of glucose also raise the specific gravity by refractometer, it remains in the physiologically possible range (1.002 to 1.035).
What is the principle of the specific gravity determination by reagent strips?
It is based on a change in pK (dissociation constant) of a polyelectrolyte on the reagent strip. The polyelectrolyte ionizes in proportion to the number of ions in solution, causing a color change in the indicator.
Advantage: measures only ionic values, so it is not affected by large organic molecules like glucose or x-ray dyes
Protein does increase the results slightly because proteins are anions.
Are specific gravity by reagent strip and by refractometer the same?
No.
[Substances in the urine that do not ionize, such as glucose, x-ray dyes, dextran, or other HMW IV fluids (plasma expanders), will increase the SG by refractometer but not by reagent strip.]
Which measurement is more accurate - specific gravity by refractometer or specific gravity by reagent strip?
Specific gravity by reagent strip.
(It is the ionic solute that reflects the concentrating ability of the kidneys, and the reagent strip detects only ionic solute. It is not affected by the presence of the non-ionic solutes that falsely elevate specific gravity by refractometer.)
How does urine pH affect specific gravity by reagent strip?
Specimens with a pH of 6.5 or higher have decreased readings because of interference with the color indicator.
(Reagent strip manufacturers recommend adding 0.005 to specific gravity readings when the pH is 6.5 or higher.)
What is normal daily urine volume?
1200 to 1500 mL
What is the normal ratio of day to night urine volume?
3:1
What is diuresis?
INCREASED urine production
What is polyuria?
Urine production over 2000 mL per day.
What is oliguria?
Urine production less than 500 mL per day.
What is anuria?
NO urine production
How is the volume of urine produced affected by diabetes mellitus?
It is INCREASED because of solute diuresis.
(The kidneys do not reabsorb the excess glucose, so increased amounts of water must be excreted to remove the glucose from the body. The SG of the urine is high because of the glucose present.)
How is the volume of urine produced affeced by diabetes insipidus?
It is INCREASED.
(The deficiency of ADH results in less water reabsorption in the renal tubules. The SG of the urine is low.)
DI = decreased SG but high urine volume
How do some laboratories check the completeness of a 24-hr urine specimen?
By measuring the urine creatinine.
(Values less than 1 gram/24 hours indicates an incomplete collection.)
What is responsible for the color of normal urine?
Primarily urochrome, a yellow pigment, and to a lesser extent, uroerythrin (red) and urobilin (orange-red).
What might cause the urine to be almost colorless (straw)?
Dilute urine
What are some causes of amber urine?
high specific gravity
bilirubin
large doeses of vitamin A
pyridium
nitrofurantoin
If a urine develops a yellow foam on top when it is shaken, what abnormal test result would be expected on the reagent strip?
A positive bilirubin
What might cause the urine to be yellow-green?
Bilirubin oxidized to biliverdin.
What are some causes of red urine?
blood
hemoglobin
myoglobin
porphyrins
beets
What might cause the urine to be black or brown?
melanin
homogenistic acid
RBCs oxidized to methemoglobin
When is melanin present in urine?
metastatic melanoma
(It turns the urine dark brown or black.)
When is homogentisic acid present in the urine?
With alkaptonuria, an inborn error of metabolism.
(An enzyme deficiency prevents the phenylalanine-tyrosine pathway from going to completion, and homogenistic acid accumulates in the blood, tissues, and urine. Homogentisic acid turns the urine black on standing and causes a positive reaction in the copper reduction test.)
What might cause the urine to be port wine colored?
Porphyrins
(Porphyrins are an intermediary in the synthesis of heme. Porphyrinuria may be seen in a variety of disorders, including lead poisoning, iron deficiency, liver disease, renal disease, and genetic disorders that result in a deficiency of one of the enzymes required for the synthesis of heme.)
What might cause the urine to be smoky in appearance?
RBCs
What might cause the urine to be cloudy?
WBCs, RBCs, epithelial cells, mucus, bacteria, and crystals
What would cause a strong ammonia odor in a urine specimen?
UTI or an old specimen.
(The odor is due to ammonia from the breakdown of urea by bacteria. Odor is not reported.)
What causes the urine to smell fruity?
Ketones
(Often present in urine of diabetics whose glucose is not in control.)
Under CLIA’88, what is the level of complexity for urinalysis by reagent strip or tablet?
Waived
How should reagent strips for urine testing be stored?
In their original container with a desiccator, tightly capped, and at room temperature.
A urine specimen for routine urinalysis has been refrigerated overnight. Prior to testing, what 2 things should be done to the specimen?
(1) brought to room temperature
(2) thoroughly mixed
(The enzymatic reactions on the reagent strips may be inhibited if the urine is cold, and false-negative results may be obtained if RBCs and/or WBCs have settled to the bottom of the specimen container.)
Under CLIA’88, how often must controls be run on reagent strips?
2 levels of controls (pos and neg) must be run every 24 hours AND whenever a new bottle of reagent is opened.
(Distilled water is NOT recommended as a negative control because reagent strip reactions are designed to perform at an ionic concentration consistent with urine.)
A technologist notices that a urine specimen is intensely colored. Why is this an important observation?
Intensely colored urines may result in false-positive reagent strip reactions with automated readers.
What are the normal values for the tests on the urine reagent strip?
pH: (random urine) 4.5-8.0
pH: (first AM) 5-6
protein: negative or trace
blood: negative
nitrite: negative
leukocyte esterase: negative
glucose: negative
ketones: negative
bilirubin: negative
Urobilinogen: less than/equal to 1 EU/dL
How does a vegetarian diet affect the urine pH?
It produces an alkaline urine.
Why is the test for protein included in a routine urinalysis?
It is an early indicator of renal disease.
What is the principle of the protein test on the reagent strip?
Protein error of indicators
(A buffer in the reagent pad maintains the pH at 3, a pH at which the indicator should be yellow; however, if protein is present, the indicator changes to green or blue.)
How could the protein reaction be adversely affected by dipping the reagent strip in the urine too long?
If the citrate buffer is washed out, a FALSE POSITIVE occurs because the pH of the urine causes a color change in the indicator.
Which protein(s) does the reagent strip detect?
Albumin
Which proteins are detected by acid precipitation tests for protein?
Albumin
Globins
Bence Jones proteins
Which acid is commonly used to precipitate urine protein?
Sulfosalicylic acid (SSA)
(Should be performed on the supernatant of a centrifuged urine to avoid false-positive reactions. Some labs perform SSA testing only on highly alkaline urines since these can overcome the acid buffer system of the reagent strip and cause false-positive results.)
What are some causes of false-positive results in protein precipitation tests?
turbidity
radiographic contrast media
some drugs - penicillin, sulfonamides, cephalosporins, and tobutamide
How does the preservative thymol interfere with urinalysis tests?
It can cause false-positive protein in acid precipitation tests
What might account for a positive protein precipitation test with a negative reagent strip protein?
A protein other than albumin, such as Bence-Jones protein.
(This discrepancy could also be due to a false-positive precipitation test.)
How can a highly buffered alkaline urine cause erroneous protein results?
It can cause a FALSE NEGATIVE precipitation test by neutralizing the acid reagent.
It can also cause a FALSE POSITIVE protein on reagent strip if the citrate buffer is overcome and the pH of the reagent square increased. The increased pH would cause the pH indicator to change color.
What are Bence-Jones proteins?
Free immunoglobulin light chains, either kappa or lambda.
(They may be present in the urine of patients with multiple myeloma and Waldenstrom’s macroglobulinemia.)
What are the solubility characteristics of Bence-Jones proteins?
They precipitate at 40-60*C and redissolve at 100*C.
(The usual method of detecting Bence Jones proteins is urine electrophoresis. They appear as a peak in the gamma region. Immunofixation will determine the light chain specificity [kappa or lambda]).
A patient’s serum demonstrates an M-spike in the gamma region on serum protein electrophoresis. His urine also shows a spike in the same region. An intern notices that the protein was negative on the urinalysis report and calls the lab to point out the discrepancy. What is the explanation for this apparent discrepancy.
The reagent strip only detects albumin.
(An acid precipitation test for protein would be positive with Bence-Jones protein.)
What is orthostatic proteinuria?
A benign proteinuria most commonly seen in young adults. Protein is negative in the first AM urine, but becomes positive after the patient has been standing.
A patient is instructed to collect a 24 hour urine for a quantitative protein test. The patient begins collecting urine on Monday morning at 6 AM. Subsequent specimens collected at 10 AM, 1 PM, 5 PM, and 11 PM Monday and the 6 AM specimen on Tuesday are added to the container. How will the results of the quantitative protein test be affected?
The results will be falsely elevated because this is actually more than a 24 hour collection.
(The 6 AM Monday collection should have been discarded.)
What reagents are used in the glucose test on the reagent strip?
Glucose oxidase/peroxidase
What sugar(s) does the reagent strip detect?
The reagent strip is specific for glucose.
What is the significance of a positive urine glucose?
It usually indicates an elevated blood glucose and is commonly seen in uncontrolled diabetes.
If a patient has glucose in his urine, what is probably true about his blood glucose level?
It is probably above 160-180 mg/dL, the average renal threshold for glucose.
What is the name of the condition in which glucose is excreted in the urine when the blood sugar is within the normal range?
Renal glucosuria
(A defect in the renal tubules’ ability to reabsorb glucose.)
Why is urine testing not recommended as a screen for diabetes mellitus?
Some diabetics develop an elevated renal threshold, so they can have a negative urine glucose even when their blood sugar is elevated. Blood tesing is more sensitive for the detection of diabetes mellitus.
What effect would contamination of the urine container with oxidizing detergents or bleach have on the glucose test results by reagent strip?
It would result in a false positive glucose.
(The blood reaction would also be a false positive.)
Which is more specific for glucose, the reagent strip or the copper reduction test?
The reagent strip.
(The copper reduction test reacts with all reducing sugars [glucose, galactose, fructose, lactose, and pentose]. Uric acid, creatinine, homogentisic acid, ascorbic acid, chloroform, and formaldehyde are non-sugar reducing substances that also react in the copper reduction test.)
What is “pass through” with the copper reduction test?
When the urine glucose is greater than 2 g/dL, the color changes to bright orange and then back to dark greenish-brown.
(Unless the reaction is watched, the result will be mistakenly recorded as negative. The test should be repeated using the 2-drop method.)
In instructing a student in the performance of a copper reduction test, what safety precautions should be mentioned?
Because the tablets contain NaOH, they should not be picked up with the hands, and the test should be carried out in a tube placed in a test tube rack because heat is generated in the reaction.
Why are urine samples from pediatric patients (up to 2 years old) tested by the copper reduction test?
To screen for galactosemia.
(Galactose is a reducing substance.)
What might cause a positive urine glucose oxidase test and a negative test for reducing sugars?
Since glucose is a reduing sugar, it should be detected by both methods. In this case, the glucose level must be below the sensitivity of the copper reduction test.
Name the 3 ketones.
(1) Acetone
(2) acetoacetic acid (diacetic acid)
(3) beta-hydroxybutyric acid (beta-hydroxybutyrate)
What is the significance of positive urine ketones?
Ketones in the urine are a sign of impaired carbohydrate metabolism and an indication that fats are being used as the primary source of energy. Ketones are seen in the urine with uncontrolled diabetes mellitus, low carbohydrate diets, vomiting, and starvation.
What reagent is used to detect ketones on reagent strip?
Sodium nitroprusside
Laboratory tests for ketones are usually most sensitive to which ketone?
Acetoacetic acid
A patient’s urine is positive for glucose and ketones. What further testing should be performed?
Blood glucose
(The urine results are suggestive of uncontrolled diabetes mellitus.)
What can result in a false-negative urine ketone test?
An improperly stored specimen.
(Acetoacetic acid is converted to acetone, which is lost through evaporation.)
What reagent is used to detect bilirubin on reagent strips?
Diazonium salts
Atypical color reactions are observed on the bilirubin pad on the reagent strip. What other test could be done?
Ictotest
(It is less subject to interference and is more sensitive than the reagent strip.)
A newly hired technologist cannot find the mats for the Ictotest and performs the test on a paper towel. Will the results be valid?
No
(The mat has special absorbant properties that cause bilirubin to remain on the surface as the urine absorbs into the mat.)
What is the significance of a positive urine bilirubin?
Hepatic or post-hepatic jaundice
Which type of bilirubin can be excreted in urine?
Only conjugated (direct) bilirubin.
What is the significance of an increased urine urobilinogen?
Pre-hepatic or hepatic jaundice.
A positive urine bilirubin with a negative urobilinogen is suggestive of what condition?
obstructive jaundice (post-hepatic)
A patient’s urine is negative for bilirubin. The urobilinogen is 4 E.U. These findings are suggestive of what condition?
A pre-hepatic jaundice, such as hemolytic anemia.
What is the appropriate test to perform to detect a decreased urine urobilinogen?
A quantitative urine urobilinogen.
(The reagent strip only detects increased amounts.)
What is the preferred specimen for a urine urobilinogen?
A 2-hour specimen collection between 2-4 PM when urobilinogen excretion is highest.
What reagent is used to detect urobilinogen in the quantitative test?
Ehrlich’s reagent, paradimethylaminobenzaldehyde
(This reagent also reacts with porphobilinogen. The urine should be at room temperature to avoid false positives caused by the warm aldehyde reaction.)
How should a specimen for urobilinogen be stored?
In a dark container because urobilinogen is light sensitive.
A physician suspects that his patient is in the early stage of liver disease. The urinalysis shows slightly increased urobilinogen, but the bilirubin is negative. What might cause these results and what further urine testing should be performed?
Urobilinogen is a more sensitive indicator of liver disease than bilirubin.
An Ictotest should be performed on the urine since it is more sensitive to bilirubin than the reagent strip test.
A serum bilirubin and liver enzymes should be ordered.
Which substances in the urine are light sensitive?
Bilirubin and urobilinogen
What reagents are used in the blood test on the reagent strip?
The test is based on the peroxidase-like activity of hemoglobin.
The reagents on the strip are peroxidase and a chromogen.
(The second step in this reaction is similar to that of the glucose oxidase test.)
What substances will cause a positive blood test on the reagent strip?
RBCs, hemoglobin, and myoglobin
What is the significance of a positive urine nitrite?
Urinary tract infection by nitrate-reducing bacteria
What are some factors that can casue false-positive nitrite tests?
Less than 4 hour incubation time in the bladder
insufficient dietary nitrate
large quantities of ascorbic acid
degradation of nitrite to nitrogen
What is the significance of a positive urine leukocyte esterase (LE) test?
It indicates the presence of neutrophils, which in large numbers usually indicates a urinary tract infection.
Advantage: its ability to detect esterase even if the cells have lysed and are not visible by microscopy.
(Note: lymphocytes are not detected by the LE test because they do not produce esterase.
How can porphobilinogen and urobilinogen be differentiated in the Watson-Schwartz test?
By extractions with chloroform and butanol.
Urobilinogen = soluble in both
Porphobilingoen = insoluble in both
What is the Hoesch test?
A rapid method to detect porphobilinogen that does not require a separation phase.
2 drops of urine + 1-2 mL of Ehrlich’s reagent = red color at the top of the solution indicates presence of porphobilinogen
Which stain can be used for urine sediment examination?
Sternheimer-Malbin
Which types of microscopes provide the best differentiation of formed elements?
Phase contrast and interference contrast
(Elements such as hyaline casts, mucus, and bacteria are easier to see with these microscopes.)
What is the significance of epithelial cells in the urine sediment?
Squamous and transitional epithelial cells are seldom important.
Renal epithelial cells are a sign of renal tubular necrosis.
Which type of WBC is most frequently present in the urine sediment with urinary tract infections?
Segmented neutrophils (polys)
What is the significance of clumped WBCs in the urine sediment?
WBC clumps are a sign of an active infection.
What are glitter cells?
WBCs whose granules demonstrate Brownian movement.
(Seen in hypotonic urine and stain faintly or not at all with the Sternheimer-Malbin stain.
What is the clinical significance of oval fat bodies in the urine sediment?
Oval fat bodies are fat-filled renal tubular epithelial cells.
They are a sign of tubular necrosis and are seen with nephrotic syndrome.
Oval fat bodies can be confirmed with polarized light or Sudan stains.
With polarized light, the lipids will demonstrate the characteristic Maltese cross formation.
What is the clinical significance of RBCs in the urine sediment?
They may be the result of damage to the glomerular membrane or vascular injury in the GU tract.
In females, they may also be contaminants from menstruation.
What are dysmorphic RBCs?
They are RBCs that vary in size, have bizarre shapes, or are fragmented.
They are a sign of glomerular bleeding.
What might cause lysis of RBCs in the urine sediment?
Alkaline or hypotonic urine
What are ghost cells?
RBCs that have lost their hemoglobin.
(Seen in hypotonic or alkaline urine)
What are casts?
Protein molds of the renal tubules.
(They are characterized by parallel sides and rounded ends.)
What protein is found in all casts?
Tamm-Horsfall protein
Pathological casts (granular, cellular, or waxy) contain albumin as well.
Hyaline casts have Tamm-Horsfall only.
Where are casts formed?
In the distal convoluted tubules and collecting ducts.
List the order or progression in the aging of casts.
Cellular => Granular => Waxy
What is a cylindroid?
A cast with a tapering end.
It is formed at the junction of the ascending loop of Henle and the distal convoluted tubule.
What is the clinical significance of hyaline casts in the urine sediment?
Hyaline casts are the most common and least significant of the casts.
0-2/LPF are normal
Higher numbers may be seen transiently with: stress, exercise, and trauma.
Large numbers (20-30/LPF) may be seen in renal disease.
What is the clinical significance of WBC casts in the urine sediment?
They are associated with pyelonephritis.
The finding is significant because it differentiates upper urinary tract infection from lower urinary tract infection.
What is the clinical significance of RBC casts in the urine sediment?
Glomerulonephritis
(The finding is significant because it pinpoints the kidneys as the source of the bleeding.)
What is the clinical significance of hemoglobin casts in the urine sediment?
They have the same significance as RBC casts.
(Glomerulonephritis. Pinpoints the kidneys as the source of bleeding.)
What is the clinical significance of epithelial cell casts in the urine sediment?
Renal tubular damage
The only epithelial cells seen in casts are renal epithelial cells.
(Transitional and squamous epithelial cells are found in the ureters and urethra and therefore cannot be incorporated into casts, which form in the renal tubules.)
What is the clinical significance of granular casts in the urine sediment?
0-1/LPF is considered normal
Increased numbers are seen in glomerulonephritis and pyelonephritis.
Granular casts may form from the degeneration of cellular casts.
What is the clinical significance of waxy casts in the urine sediment?
They are the final stage in the degeneration of cellular casts and point to severe urinary stasis.
They are only seen in advanced renal disease.
They are homogenous, refractile, and irregular in shape with blunt ends, cracks, or clefts.
Highly refractile structures with blunt ends are observed in an infant’s urine sediment and identified as waxy casts. Upon review of the results, the supervisor notes that there was no protein in the urine. What might explain these findings?
Because there is no protein in the urine, the structures must be something other than casts. Since the patient is an infant, disposable diaper fibers should be suspected.
Examination with polarized light may be helpful. Paper fibers polarize light; casts do not.
Paper fibers may also be seen in the urine of incontinent adults who wear bladder protection pads.
What is the clinical significance of fatty casts in the urine sediment?
They are associated with nephrotic syndrome.
What is the clinical significance of broad casts in the urine sediment?
They are a sign of dilated renal tubules, urine stasis, and advanced renal disease.
Broad casts can be of any type, but granular and waxy are most common.
Broad casts are sometimes referred to as renal failure casts.
What is the clinical significance of yeast in the urine sediment?
The yeast most often seen in urine sediment is Candida.
It may be a contaminant from the skin, GI tract, or vagina.
Candida is ovoid, 5-7 microns in diameter, and may have a single bud.
The presence of pseudohyphae points to a Candida infection. This occurs most often in immunocompromised or catheterized patients.
What is the clinical significance of bacteria in the urine sediment?
The significance depends on the type of specimen (clean-catch vs catheterized) and other findings on the urinalysis.
Bacteria without increased polys are usually contaminants, unless the patient is neutropenic.
Bacteria with polys are associated with urinary tract infections.
What is the clinical significance of Trichomonas in the urine sediment?
Trichomonas is a contaminant from the genital tract.
Trichomonas should not be reported unless motility is observed because it is difficult to differentiate non-motile Trichomonas from WBCs.
What is the clinical significance of sperm in the urine sediment?
Usually none unless the patient is a child, in which case it could be evidence of sexual abuse.
What will most likely be seen in the microscopic examination when a pink sediment is observed in the urine centrifuge tube?
Amorphous urates
Urates are found in acid urine and precipitate as the urine cools.
They are a normal finding, but can obscure other significant elements.
Urates can be dissolved by warming the urine to 60*C.
What is the color of the precipitate formed when amorphous phosphates are present in large amounts?
White
Amorphous phosphates can be dissolved by adding 2% acetic acid.
Name the NORMAL crystals found in ACID urine.
Amorphous urates
Uric acid
Calcium Oxalate
Name the ABNORMAL crystals found in ACID urine.
Leucine
Tyrosine
Cystine
Cholesterol
Bilirubin
Name the NORMAL crystals found in ALKALINE urine.
Amorphous phosphates
Triple phosphate
Ammonium biurate
Calcium phosphate
Calcium carbonate
Describe uric acid crystals.
Of all the urinary crystals, uric acid is the most pleomorphic.
It can be 4-sided, 6-sided, star shaped, or rosette shaped.
It can also form spears or plates.
It can be red-brown, yellow, or colorless.
Uric acid is strongly birefringent with polarized light.
Which crystal is the only needle found in alkaline urine?
Calcium phosphate.
It may appear as rosettes and “pointing fingers.”
In what other forms does calcium oxalate appear besides the “envelope”?
Less commonly, it can be dumb-bell shaped or ovoid.
When ovoid, it may be mistaken for RBCs. Polarized light can help in the differentiation. Calcium oxalate crystals are strongly birefringent; RBCs are not.
An MLT student observed that several of the urine sediments he examined had irregularly round granules with central slits. What were they?
Starch granules.
They are a common contaminent in the lab if powdered latex gloves are worn.
With polarized light, starch granules produce irregular, fuzzy Maltese crosses.
What is hemosiderin?
A form of stored iron.
Hemosiderin, formed from hemoglobin by the renal tubular epithelial cells, is seen in the urine with severe intravascular hemolysis and hemochromatosis.
Unstained, it appears as coarse yellow-brown granules.
It stains blue with Prussian blue stain.
A patient had an intravenous pyelogram (IVP). How might this procedure affect the results of the patient’s urinalysis?
The specific gravity may be greater than 1.035 if measured by refractometer.
The reagent strip specific gravity would be preferred since it is not affected by radiographic dye.
The dye may be seen in the urine sediment in the form of needles and spheres and may also cause a false-positive protein by SSA.
An obese 45-year-old woman is seen in a physician’s weight loss center. She reports that she has tried a variety of diets and cannot lose weight. A urinalysis is performed and the medical assistant detects a fruity odor to the urine. What is the most likely explanation of her urinalysis results?
The presence of ketones in the urine in the absence of glucose, suggests that this woman has been on a low carbohydrate or starvation diet.
The ketones are present in the urine due to incomplete fat metabolism and cause a fruity odor.
Explain the discrepancy in the following urinalysis report.
The fact that the chemical test for bilirubin was negative and the urine was pale yellow casts doubt on the identification of the crystals.
A patient visits his physician with complaints of severe lower back pain. Do the urinalysis results suggest a possible cause for the patient’s condition?
Yes
The clumps of calcium oxalate crystals and the blood in the urine may indicate the presence of renal calculi.
A 50-year-old male who just completed a 26 mile marathon is seen in the emergency room complaining of chest pain and shortness of breath. Is there anything in the urinalysis report to cause concern?
No
The abnormal findings can be explained by the intense exercise of the marathon.
The color and specific gravity are related to dehydration; the small amount of protein and blood and the hyaline casts are common findings after a long run.
An 18-year-old girl is seen in her physician’s office due to recent rapid weight loss. The physician notes pitting edema. The patient was last seen 3 weeks ago when she was diagnosed with strep throat. Based on the urinalysis results and the patient history, what is the probable diagnosis?
Acute glomerulonephritis
This is a sterile inflammatory process that is most frequently seen in children and young adults following respiratory tract infections with certain strains of group A streptococci.
The patients develop anti-streptolysin O, which forms immune complexes with the streptolysin O exotoxin produced by the bacteria. These immune complexes are deposited on and damage the glomerular membrane.
A 24-year-old woman who just returned from her honeymoon is seen by her physician with complaints of a low-grade fever, flank pain, frequency, and dysuria. She has a history of recurrent UTIs. Based on the urinalysis results and the patient history, what is the probable diagnosis?
Pyelonephritis
The WBC casts indicate that the infection is in the kidneys.
In the absence of WBC casts, the diagnosis could have been either cystitis (bladder infection) or pyelonephritis.
A 65-year-old man is seen in the ER with shortness of breath and chest pain that radiates to his left arm. The ER physician orders an EKG, cardiac enzymes, and a urinalysis. Relate the results of the urinalysis to the patient’s symptoms.
The positive reaction for blood in the absence of RBCs, together with the positive protein and the color of the urine, suggests that myoglobin may be present.
Myoglobin reacts with the reagents in the blood portion of the reagent strip and may be detected in the urine following myocardial infarction.
To differentiate hemoglobin from myoglobin, 2.8 grams of ammonium sulfate are added to 5 mL of centrifuged urine. Hemoglobin is precipitated by ammonium sulfate. The urine is filtered and the filtrate is tested with a reagent strip. If the reaction is still positive, myoglobin is present.
A urinalysis was performed on specimens collected from an inpatient at 7 AM and 1 PM. Examine the reports and explain why they are different.
The discrepancies are related to the specific gravity of the urine.
The 7 AM urine was more concentrated and so abnormal constituents in small quantities were detectable.
Later in the day after the patient was hydrated, the urine was dilute and the small amount of protein, glucose, and blood were not detectable.
This illustrates why a first morning specimen is preferred for routine urinalysis.
A 75-year-old woman’s pre-op urinalysis was normal. Following surgery, while being transfused with a unit of RBCs, she developed fever, chills, and back pain. The transfusion was stopped and the first-voided urine was sent to the laboratory. Examine the results below and explain the changes in the urinalysis results pre- and post-transfusion.
The color of the urine and the presence of hemoglobin following transfusion point to a hemolytic transfusion reaction.
A pre-employment physical examination is performed on a 45-year-old business executive. He reports that he has been very thirsty lately and urinating more frequently than usual. Examine the results of his urinalysis. What do these findings suggest?
Diabetes mellitis
With DM, the urine volume is increased and the glucose in the urine causes a high specific gravity.
Ketones are present because the body metabolizes fats for energy, instead of carbohydrates.
The fact that this patient also has protein and granular casts in the urine points to renal disease, a common complication of diabetes.
How are cell counts usually performed on body fluids?
Body fluid cell counts have traditionally been performed in a hemacytometer, usually by counting the cells in all 9 square millimeters on both sides.
What is a transudate?
An effusion due to a systemic disease process that affects fluid filtration and reabsorption, such as CHF, hypoalbuminemia, and cirrhosis of the liver.
The underlying disorder is outside of the body cavity where the fluid accumulates.
What is an exudate?
An effusion due to an inflammatory process within the body cavity, such as an infection, inflammation, malignancy, or hemorrhage.
How can transudates and exudates be differentiated?
What are mesothelial cells?
Cells that line the body cavities.
They can be seen in normal body fluids and appear in singles, pairs or sheets.
They are homogenous cells of uniform size (12-20 microns), and there is a slit-like opening between cells so that each retains its individuality.
The cytoplasm is basophilic and abundant and may have vacuoles. Mesothelial cells may be multinucleated.
What are histiocytes?
Macrophages
They are found in normal fluids.
15-30 microns
Cytoplasm: abundant, colorless, may contain many vacuoles and ingested material
Nucleus: eccentric with delicate chromatin
Describe malignant cells.
Great variation in size
Scant cytoplasm
irregularly shaped
Tendency to fuse with other cells
Often have multiple nuclei (vary in size)
Nuclear chromatin is condensed and nucleoli, mitotic figures, and nuclear molding is typical
Why are 3 tubes of CSF collected and numbered during a lumbar puncture?
So that the specimen can be distributed to different departments, depending on the order of collection.
Tube #1: most likely to have contaminating bacteria and RBCs from traumatic tap = it is used for chemistry and serology tests
Tube #2: sent to microbiology for gram stain and culture
Tube #3: sent to hematology for cell count and differential (since it is least likely to contain blood cells due to the tap)
What is xanthochromia?
A yellow, pink, or orange discoloration to the CSF due to oxyhemoglobin and/or bilirubin from lysed RBCs.
Xanthochromia is seen in subarachnoid hemorrhage.
The CSF should be examined within 1 hour of collection to avoid a false positive from in vitro hemolysis of RBCs.
The CSF is centrifuged, and the color of the supernatant is compared to a tube of water. The tubes should be examined against a white background.
What are the typical CSF findings in bacterial meningitis?
The fluid may appear cloudy.
WBCs are increased (predom. polys)
Glucose is decreased
Protein and lactate are increased.
What are the typical CSF findings in viral meningitis?
WBCs increased (predom. lymphs)
Protein increased
Glucose and lactate = normal
What are the typical CSF findings in fungal meningitis?
WBCs increased (lymphs & monos)
Protein and lactate are increased
Glucose may be decreased
The laboratory findings with mycobacterial meningitis most closely resembles those of which other type of meningitis?
Fungal meningitis
However, a unique characteristic that may be observed with mycobacterial meningitis is the presence of a web-like clot or pellicle in the CSF
What would the presence of nucleated RBCs in the CSF indicate?
Bone marrow contamination during specimen collection
What are the 4 classifications of synovial fluid, based on results of laboratory testing?
(1) Non-inflammatory (e.g., degenerative joint disease)
(2) Inflammatory (e.g., RA, LE, crystal-induced [gout, pseudogout])
(3) Infectious (e.g., bacterial)
(4) Hemorrhagic (e.g., trauma, coagulation abnormalities)
Name several conditions that can alter the color of synovial fluid.
Infection
Crystals
Hemorrhage
Name several conditions that can cause synovial fluid to be cloudy.
Inflammation
Infection
Crystals
Hemorrhage
How is synovial fluid examined for crystals?
A wet prep of the fluid is examined under polarized light.
Which are the 2 most common crystals seen in synovial fluid?
Monosodium urate - seen in gout
Calcium pyrophosphate - seen in pseudogout
Urate crystals are strongly birefringent needles.
Calcium pyrophosphate crystals are rod-shaped, rectangular, or rhomboid and are weakly birefringent.
What is the foam stability index (shake test)?
A test to assess fetal lung maturity.
Amniotic fluid is shaken with 95% ethanol and allowed to sit undisturbed for 15 minutes.
The surface of the fluid is observed for the presence of a continuous line of bubbles around the outside edge.
The presence of bubbles correlates with fetal lung maturity, although the analysis is subjective.
What are lamellar body counts (LBC)?
Another test for fetal lung maturity.
Lamellar bodies are lamellated phospholipids.
The number in the amniotic fluid correlates with the amount of phospholipid in the fetal lungs.
Counts are obtained from the platelet channel of hematology analyzers.
Samples must be free of contamination by blood and meconium.
How is semen cell count performed?
The semen is diluted with sodium bicarbonate and formalin to immobilize and preserve the sperm.
They are counted in a Neubauer hemacytometer.
What are some morphological abnormalities of sperm?
Double heads, giant heads, amorphous heads, pinheads, tapering heads, constricted heads, double tails, coiled tails, and large numbers of spermatids.
The Papancolaou stain is recommended.
At least 200 cells should be examined.
What is the principle of the fecal occult blood test (FOBT)?
It is based on the pseudoperoxidase activity of hemoglobin.
Hemoglobin reacts with hydrogen peroxide. The liberated oxygen oxidizes a chromogen, which results in a color change.
