urinalysis Flashcards
What is a clean catch urine ssample
collected midstream
Methods of urine collection
random collection is taken at any time of day with no precautions (urine may be dilute, isotonic or hypertonic), eraly morning sample before ingestion of fluids (hypertonic), catheterization of bladder or suprapubic needle aspiration of bladder
What causes foul, sweet, fruity or maple-syrup like smelling urine
Foul, offensive: Old specimen, pus or inflammation. Sweet: Glucose. Fruity: Ketones. Maple syrup-like: (Maple Syrup Urine Disease)
What causes deep yeelo, yello-green, red, brownish-red and brownish-black colored urine?
Deep Yellow: Concentrated Urine, Riboflavin. Yellow-Green: Bilirubin / Biliverdin. Red: Blood / Hemoglobin. Brownish-red : Acidified Blood (Acute GN). Brownish-black: Homogentisic acid (Melanin)
How is glucose detected by urine dipstick?
Glucose oxidase converts glucose + water and O2 to gluconic acid and peroxide. Then, Horseradish peroxidase converts peroxide + KI (also on the strip) to KIO3 and water, then the oxygen liberated binds with dye forming a colored substrate
False negative glucose urine dipstick
As ascorbic acid is an oxygen acceptor and most likely to be present in large amounts in the urine of pregnant women, this will cause a false-negative result. Also, this can not detect sugars other than glucose, so not beneficial in newborn screens
Another method used to detect sugars
CuSO4 can detect reducing sugars: Galactose (galactosemias), fructose (fructose intolerance), lactose (lactase deficiency), pentoses (essential pentosuria), maltose (non-pathogenic). NOT sucrose b/c it is not reducing
How is bilirubin detected by urine dipstick?
Bilirubin combines with a diazo salt in an acidic medium to form azobilirubin which forms a light-dark tan color.
False negative and positive bilirubin are caused by…
Indican (indoxyl sulfate) will cause a false-positive result, while ascorbate will cause a false-negative result
Limitations of urine bilirubin dipstick
Only measure direct bilirubin (which correlates with urobilinogen and serum bilirubin), not indirect. Interference can occur with prolonged exposure of sample to light.
Other methods for measuring bilirubin
Ictotest (more sensitive tablet version of same assay) and serum test for total and direct bilirubin
How are ketones detected by urine dipstick?
The ketones (acetoacetate) reacts with nitroprusside to form a purple color Also detects acetone but not beta-hydroxybutyrate
What causes ketones in urine
Diabetic ketosis or other form of calorie deprivation
Limitations of urine ketone detection
Interference can occur with expired reagents(due to degradation with exposure to moisture in air) and it only measures acetoacetate, not other ketone bodies.
Other methods for urine keytone detection
Ketostix (more sensitive tablet version of same assay) and serum glucose measurement to confirm Diabetic ketoacidosis.
How is specific gravity measured by urine dipstick?
by measuring the change in pKa of polyelectrolytes in relation to ionic concentration
What is the normal range for urine specific gravity
1.003-1.035
Uses and limitations of urine specific gravity
Useful for diabetes insipidus. Limitations: alkaline urine interferes with test and does not measure non-ionized solutes such as glucose.
Other methods for urine specific gravity detection
refractometry, hydrometer, osmolality measurement
What will show up as a positive in the urine blood dipstick
RBCs, free hemoglobin or free myoglobin. While hemoglobin and RBCs are normally too large to pass through glomerulus, myoglobin passes freely through glomerulus.
How is blood detected by urine dipstick
pseudoperoxidase reaction, which is more sensitive to hemoglobin and myoglobin than intact RBCs.
Describe urine in hematuria vs hemoglobinuria
In cases of hematuria, the urine is red and cloudy, but will clear if centrifuged.Hemoglobinuria will have reddish brown urine that does not become clear after centrifugation
Normal range of urine pH, and causes of high/low pH
Normal is 4.5-8.0. Acidic urine 8.0 occurs in renal tubular acidosis.
Interference of urine pH test
bacterial overgrowth (alkaline or acidic), or “run over effect” effect of protein pad on pH indicator pad where buffers from protein area of strip spill over to pH area and make pH appear more acidic than it really is.
Other methods for urine pH
Acidity titer and blood gases
define proteinuria
> 150mg/ day protein in urine.
How are proteins measured by urine dipstick and its limitations
Bromophenol blue is used as an indicator dye. It is most sensitive to albumin and interference occurs with highly alkaline urine.
Other tests for urine protein detection
sulfosalicylic acid can detect albumins, globulins, and Bence Jones protein. Urine protein electrophoresis
Which proteins can be found in normal urine
albumin, Tamm-Horsfall, immunoglobulins, secretory IgA all at small amounts
What is urobilinogen
Urobilinogen is formed by intestinal bacteria from the breakdown of conjugated bilirubin, and it is usually excreted in feces. However a small amount may be reabsorbed and excreted in urine
How is urobilinogen detected on urine dipstick
based on a modified Ehrlich reaction, in which p-dimethyl amino benzaldehyde in conjunction with a color enhancer reacts with urobilinogen in a strongly acid medium to produce a pink-red color. A positive test response indicates normal enterohepatic circulation of biliary pigments. High concentrations of biliary pigments may occur in hemolytic crisis, or cases of hepatic or intestinal dysfunction. Low indicaties bile obstruction
Causes of a false positive and false negative urobilinogen urine test
A false positive test result may occur if the temperature of the reagent strip is elevated. A false negative test result may occur if there is formalin residue in the collection container, or if the sample is old, because urobilinogen is very unstable when exposed to light and air.
What causes nitrites in the urine
A positive nitrite test indicates that bacteria may be present in significant numbers in urine. Gram negative rods such as E. coli are more likely to give a positive test.
What causes positive leukocyte esteraste in urine
A positive leukocyte esterase test results from the presence of white blood cells either as whole cells or as lysed cells. If negative, there is no need t loo for further signs of infection
Causes of false positive and false negative leukocyte esterase in urine
False positive test results also may occur in the event of vaginal contamination. False negative test results may develop if the patient has been treated with high doses of antibiotics. Glucosuria or increased urine specific gravity may cause false negative test results
Preservation of cells/casts for microscopic analysis
Cells and casts begin to disintegrate in 1 - 3 hrs. at room temp. Refrigeration for up to 48 hours (little loss of cells).
For a high power field, what is the definition of abnormal: erythrocytes, leukocytes, renal tubular cells , bacteria, neutrophils
Per high power field (400x): > 3 erythrocytes, >5 leukocytes, >2 renal tubular cells, >10 bacteria, >1 neutrophil per 3 HPF
For low power field, what is the definition of abnormal: hyaline/granular casts, squamous cells, RBC/WBC casts
per low power field (200x): >3 hyaline casts or >1 granular cast, >10 squamous cells (contamination), any number of RBC/WBC casts
Causes of hematuria and dysmorphic RBCs
glomerular damage, tumors which erode the urinary tract anywhere along its length, kidney trauma, urinary tract stones, renal infarcts, acute tubular necrosis, upper and lower urinary tract infections, nephrotoxins, and physical stress and contamination. dysmorphic RBCs are found in glomerular disease where passage through abnormal glomerulus distorts the RBC shape
Oval fat bodies
renal tubular epithelial cells that contain numerous fat droplets and exhibit a Maltese cross configuration by polarized light microscopy
Where are casts formed
distal convoluted tubule or the collecting duct
What are hyaline casts
composed primarily of a mucoprotein (Tamm-Horsfall protein) secreted by tubule cells. The Tamm-Horsfall protein secretion, forms hyaline casts in the distal collecting duct. Most casts are made of Tamm-Horsfall mucoprotein
Factors favoring protein cast formation
low flow rate, high salt concentration, and low pH, all of which favor protein denaturation and precipitation, particularly that of the Tamm-Horsfall protein.
Cylindroids
Protein casts with long, thin tails formed at the junction of Henle’s loop and the distal convoluted tubule
What are granular and waxy casts? Broad casts?
When cellular casts remain in the nephron for some time before they are flushed into the bladder urine, the cells may degenerate to become a coarsely granular cast, later a finely granular cast, and ultimately, a waxy cast They are derived from renal tubular cells and are seen in end stage chronic renal disease
Telescoped urinary sediment and what cuases is
red cells, white cells, oval fat bodies, and all types of casts are found in more or less equal profusion. 1) lupus nephritis 2) malignant hypertension 3) diabetic glomerulosclerosis, and 4) rapidly progressive glomerulonephritis
Causes of fatty casts
nephrotic syndrome
Normal crystals and abnormal crystals
Normal: calcium oxalate, triple phosphate crystals and amorphous phosphates. Uncommon/abnormal: cystine crystals in urine of neonates with congenital cystinuria or severe liver disease, tyrosine crystals with congenital tyrosinosis or marked liver impairment, or leucine crystals in patients with severe liver disease or with maple syrup urine disease.
