CMT Urinalysis and Body Fluids Flashcards

A urine reagent strip shows a strongly positive blood reaction, but microscopy reveals no RBCs, and the patient's serum is clear with markedly elevated CK. What is the most likely cause?

Answer: Myoglobinuria from rhabdomyolysis

Myoglobin is peroxidase-active and clears rapidly from plasma, so serum stays clear while CK rises after muscle injury.

A patient taking high-dose vitamin C supplements may show which reagent strip error?

Answer: False-negative glucose and blood

Ascorbic acid is a strong reducing agent that interferes with the peroxide-based oxidation reactions for glucose and blood.

Broad, waxy casts with cracked edges in a urine sediment most strongly suggest which condition?

Answer: Chronic renal failure with extreme urine stasis

Waxy and broad casts form in dilated, stagnant tubules and indicate advanced chronic renal disease.

According to Light's criteria, which finding classifies a pleural fluid as an exudate?

Answer: Fluid-to-serum protein ratio greater than 0.5

A fluid/serum protein ratio above 0.5 (or LD ratio above 0.6) indicates an exudate.

Three tubes of CSF are collected; all three are uniformly bloody and the supernatant is xanthochromic after centrifugation. This best indicates:

Answer: Subarachnoid hemorrhage

Even blood distribution across tubes plus xanthochromia from hemoglobin breakdown points to a true intracranial bleed.

Synovial fluid examined with a compensated polarizing microscope shows needle-shaped crystals that are yellow when aligned parallel to the slow ray. These are:

Answer: Monosodium urate

Monosodium urate crystals are needle-shaped and negatively birefringent (yellow parallel), diagnostic of gout.

The reagent strip specific gravity pad detects ionic concentration through which principle?

Answer: Change in pKa of a polyelectrolyte releasing hydrogen ions

Ions in urine cause a pretreated polyelectrolyte to release H+, changing the color of a pH indicator.