MLPAO Urinalysis and Body Fluids Case Studies

Question 1

A urine dipstick shows 3+ blood but microscopic examination reveals no red blood cells. What is the most likely explanation?

Accepted Answer

Hemoglobinuria or myoglobinuria — free hemoglobin or myoglobin in urine causes a positive dipstick without intact RBCs

Answer

A positive blood dipstick without microscopic RBCs indicates hemoglobinuria (from intravascular hemolysis) or myoglobinuria (from rhabdomyolysis). Both hemoglobin and myoglobin contain heme groups that catalyze the dipstick peroxidase reaction. Serum examination (pink/red = hemolysis; clear = myoglobinuria) and CK levels help differentiate.

Question 2

A CSF specimen shows 500 WBC/µL with 95% neutrophils, protein 2.5 g/L, and glucose 1.0 mmol/L (serum glucose 6.0 mmol/L). What is the most likely diagnosis?

Accepted Answer

Bacterial meningitis

Answer

This CSF profile is classic for bacterial meningitis: markedly elevated WBC (500/µL) with neutrophil predominance (95%), significantly elevated protein (2.5 g/L), and markedly decreased glucose (1.0 mmol/L; CSF/serum ratio 0.17, well below the 0.4 threshold). Gram stain and culture are essential. Empiric antibiotics should be started immediately.

Question 3

A patient's urine shows many waxy casts, broad casts, and RTE cells. What does this suggest?

Accepted Answer

Severe chronic renal disease with tubular damage and stasis

Answer

Waxy casts indicate prolonged urinary stasis in damaged tubules. Broad casts ('renal failure casts') form in dilated, damaged collecting ducts. Renal tubular epithelial (RTE) cells indicate active tubular injury. Together, these findings suggest severe chronic kidney disease with ongoing tubular damage and a poor prognosis.

Question 4

A pleural fluid analysis shows protein 45 g/L, LDH 500 U/L (serum LDH 200 U/L), glucose 2.0 mmol/L, and many lymphocytes. What diagnosis should be considered?

Accepted Answer

Tuberculous pleuritis or malignancy

Answer

This is an exudative effusion (high protein, LDH ratio >0.6) with lymphocyte predominance and low glucose. This pattern is characteristic of either tuberculous pleuritis or malignancy. Adenosine deaminase (ADA) levels >40 U/L support TB diagnosis. Cytology and pleural biopsy may be needed for malignancy diagnosis. AFB culture and NAAT for TB should be performed.

Question 5

A urine specimen is cloudy with an alkaline pH, positive nitrite, positive leukocyte esterase, and microscopy shows many WBCs, bacteria, and triple phosphate crystals. What is the diagnosis?

Accepted Answer

Urinary tract infection likely caused by a urease-producing organism

Answer

This is a UTI caused by a urease-producing organism (likely Proteus). The urease converts urea to ammonia, creating alkaline urine that promotes triple phosphate (struvite) crystal formation. Positive nitrite confirms bacterial nitrate reduction, and positive leukocyte esterase with many WBCs confirms pyuria. Culture will likely confirm Proteus mirabilis.

MLPAO - Medical Laboratory Professionals Association of Ontario Practice Test

MLPAO - Medical Laboratory Professionals Association of Ontario Practice Test

MLPAO Urinalysis and Body Fluids Case Studies