Medical Laboratory Technician Urinalysis and Body Fluids 1 Flashcards
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A urine specimen turns dark brown-black upon standing and tests positive for reducing substances but negative for glucose by the glucose oxidase method. Which substance is most likely present?
Answer: Homogentisic acid
Homogentisic acid, excreted in alkaptonuria, oxidizes upon exposure to air and turns the urine dark brown-black. It is a reducing substance but is not detected by the glucose oxidase method, distinguishing it from glucosuria.
Which urine sediment finding is most consistent with acute tubular necrosis (ATN)?
Answer: Muddy brown granular casts
Muddy brown coarsely granular casts are the hallmark of acute tubular necrosis. They form from degenerating renal tubular epithelial cells and pigmented material, reflecting direct tubular injury.
A pleural fluid specimen has a protein concentration of 4.8 g/dL and a pleural fluid-to-serum LDH ratio of 0.7. How would this effusion be classified?
Answer: Exudate, suggesting infection or malignancy
By Light's criteria, a pleural fluid protein >3.0 g/dL or a pleural/serum LDH ratio >0.6 classifies the effusion as an exudate, which is associated with inflammatory, infectious, or malignant processes rather than hydrostatic imbalances.
A urine dipstick is strongly positive for blood, but microscopic examination reveals no red blood cells. Which of the following conditions best explains this discrepancy?
Answer: Myoglobinuria from rhabdomyolysis
The dipstick blood reaction detects heme, so it is positive for both hemoglobin and myoglobin. In rhabdomyolysis, myoglobin released from damaged muscle is excreted in urine and gives a positive dipstick reaction without intact red blood cells being present.
During a peritoneal fluid analysis, a milky white appearance is noted. Which analyte should be measured first to investigate this finding?
Answer: Triglycerides
A milky white (chylous) peritoneal effusion strongly suggests the presence of chyle from disrupted lymphatic vessels. Triglyceride measurement is the primary test; a level above 110 mg/dL confirms a chylous effusion.
A urine specimen with a pH of 8.5 and a strong ammonia odor is most likely associated with which condition?
Answer: Urinary tract infection with a urea-splitting organism
Bacteria such as Proteus mirabilis produce urease, which hydrolyzes urea into ammonia and CO2. This raises urine pH to alkaline levels (often >8.0) and produces a characteristic ammonia odor, a classic sign of infection with a urea-splitting organism.