MLT GlobeUrinalysis & Body Fluids: Urine chemical (dipstick) – page 2
49 Urinalysis & Body Fluids MCQs on Urine chemical (dipstick) with answers and explanations.
A highly alkaline urine (pH 9) may cause which error on the reagent strip protein pad?
Highly alkaline or heavily buffered urine overcomes the pad buffer and changes the indicator colour without protein, giving a false-positive result.
A urine positive with Clinitest (copper reduction) but negative with the reagent strip glucose pad most likely contains:
Copper reduction detects all reducing sugars, while the strip is specific for glucose. This pattern in an infant suggests galactosaemia and needs follow-up.
High levels of ascorbic acid in urine can cause false-negative results on which pads?
Ascorbic acid is a strong reducing agent that removes hydrogen peroxide and inhibits the peroxidase-type reactions on the blood and glucose pads. It can also affect bilirubin, nitrite and leukocyte esterase.
The reagent strip ketone pad (sodium nitroprusside) detects mainly:
Nitroprusside reacts strongly with acetoacetic acid, weakly with acetone (if glycine is present) and not at all with beta-hydroxybutyrate, the main ketone in diabetic ketoacidosis.
A positive blood pad with a uniform (non-speckled) colour, a clear red urine after centrifugation, and no red cells on microscopy is most consistent with:
Free hemoglobin or myoglobin gives uniform pad colour and red supernatant without intact RBCs. Intact RBCs give a speckled pattern and settle on centrifugation.
A patient with obstructive (post-hepatic) jaundice would most likely show which urine pattern?
Conjugated bilirubin enters urine, but bile cannot reach the intestine, so urobilinogen formation falls. Hemolytic jaundice gives negative bilirubin with high urobilinogen.
The urine bilirubin pad is based on:
Bilirubin couples with a diazonium salt in acid to form a coloured azodye. Ehrlich's reagent is used for urobilinogen on some strips.
The leukocyte esterase pad detects esterase from which cells?
Esterases are present in neutrophils, eosinophils, basophils and monocytes but not lymphocytes. The test detects intact and lysed granulocytes.
The reagent strip specific gravity pad measures:
Ions in urine release hydrogen ions from a polyelectrolyte, changing the pH indicator colour. Non-ionic solutes such as glucose and radiographic contrast are not detected.
A persistently high urine pH (above 8.0) in a fresh specimen from a patient with a UTI suggests infection with:
Urease splits urea into ammonia, making urine alkaline and favouring struvite (triple phosphate) stones. An old unrefrigerated specimen can give the same false result.
Albumin-to-creatinine ratio (ACR) is preferred to a routine dipstick for early diabetic kidney disease because:
Routine strips detect about 150–300 mg/L protein, missing moderately increased albuminuria. ACR corrects for urine concentration; KDIGO defines A2 as 30–300 mg/g (3–30 mg/mmol).
Some reagent strip manufacturers advise adding 0.005 to the specific gravity reading when the urine pH is 6.5 or higher. This is because:
The SG pad depends on release of hydrogen ions; in alkaline urine the indicator shift is blunted, so readings are falsely low. The correction compensates for this.
A urine shows many neutrophils on microscopy, but the leukocyte esterase pad is negative. The specific gravity is 1.035 and glucose is 4+. The most likely reason is:
High glucose, protein and specific gravity crenate white cells and slow esterase release, giving false-negative results. Oxidising agents cause false positives, and lysed neutrophils still release esterase.
A woman taking phenazopyridine for dysuria has bright orange urine. How does this affect reagent strip testing?
Phenazopyridine gives an orange pigment that can produce atypical colours on pads such as bilirubin, nitrite, ketone, protein and urobilinogen. Results should be confirmed by other methods.
A urine glucose pad is strongly positive, but blood glucose is normal and a repeat urine collected in a new container is negative. The first container was probably contaminated with:
Strong oxidising agents react with the chromogen directly, causing false-positive glucose (and blood) results. Ascorbic acid causes false negatives.
For the most sensitive detection of increased urine urobilinogen, a specimen is ideally collected:
Urobilinogen excretion peaks in the early afternoon, linked to the post-meal alkaline tide. First morning urine is best for nitrite and concentrated elements, not urobilinogen.
A strip is held horizontally too long after dipping, and the pH pad reads falsely low. The most likely cause is:
If excess urine is not removed, the acid buffer of the protein pad can run over onto the pH pad and lower the reading. Loss of CO2 or bacterial growth tends to raise pH.
A pregnant woman has 2+ urine glucose on a reagent strip, but her fasting plasma glucose is 4.8 mmol/L (86 mg/dL). The most likely explanation is:
Glucose appears in urine when plasma glucose exceeds the renal threshold (about 160–180 mg/dL, 8.9–10 mmol/L); in pregnancy and renal glycosuria the threshold is lower. Ascorbic acid would cause a false negative.
A urine collected in a container rinsed with a quaternary ammonium disinfectant is likely to show a false-positive result on the:
Quaternary ammonium compounds and chlorhexidine alter the protein pad's indicator and give false-positive protein. Glucose false positives are caused by oxidising agents.
A refrigerated urine is tested immediately after removal from the refrigerator. Which result is most likely to be affected?
Cold slows enzymatic reactions, so refrigerated urine should reach room temperature before strip testing. Refrigeration does not create nitrite.