MLT GlobeUrinalysis & Body Fluids: Urine chemical (dipstick) – page 3
49 Urinalysis & Body Fluids MCQs on Urine chemical (dipstick) with answers and explanations.
A woman with burning on urination has a urine that is positive for both leukocyte esterase and nitrite. This most suggests:
Leukocyte esterase indicates white cells (pyuria) and nitrite indicates nitrate-reducing bacteria; together they strongly suggest a bacterial urinary tract infection.
A non-diabetic patient with prolonged vomiting and poor food intake has positive urine ketones. The most likely reason is:
When carbohydrate intake is low, the body breaks down fat for energy and the liver produces ketone bodies, which appear in the urine even without diabetes.
A patient with constant thirst and very large urine volumes has a persistently low specific gravity of about 1.002. This most suggests:
A persistently low specific gravity with polyuria shows that the kidneys cannot concentrate urine, as in diabetes insipidus. Dehydration and contrast media give a high specific gravity.
A dipstick protein pad is negative, but sulfosalicylic acid (SSA) precipitation is positive. The most likely explanation is:
The protein pad uses the 'protein error of indicators' and reacts mainly with albumin. SSA precipitates all proteins, including immunoglobulin light chains. Alkaline urine gives false positives on the dipstick, not false negatives.
A diabetic patient in severe ketoacidosis has only a small positive urine ketone result. The best explanation is:
In severe ketoacidosis with poor tissue perfusion, the ratio of beta-hydroxybutyrate to acetoacetate rises. The nitroprusside test therefore underestimates total ketosis; a blood beta-hydroxybutyrate assay is better.
To help distinguish myoglobinuria from hemoglobinuria, the most useful finding is:
Free hemoglobin binds haptoglobin and colours the plasma pink-red in hemolysis. Myoglobin is small and cleared quickly, so plasma stays clear while CK is very high.
A urine specimen has refractometer specific gravity 1.040 but reagent strip specific gravity 1.015. The patient recently had an intravenous pyelogram. The best explanation is:
Non-ionic contrast media increase refractive index but do not affect the ionic strip pad. Refractometer values above about 1.040 in a normal urine suggest contrast or other high-molecular-weight substances.
A patient on cyclophosphamide therapy also receives MESNA. The urine ketone pad is positive although there is no ketosis. The best explanation is:
Compounds with free sulfhydryl groups, such as MESNA and captopril, react with nitroprusside and give false-positive ketone results. The pad does not detect beta-hydroxybutyrate.
A patient with acute abdominal pain and confusion has a strongly positive urine Ehrlich reaction. Which test distinguishes porphobilinogen from urobilinogen?
Ehrlich's reagent reacts with both urobilinogen and porphobilinogen; the Watson-Schwartz test uses solvent extraction to tell them apart, and the Hoesch test is a rapid PBG screen. Acetest detects ketones.