MLPAO Urinalysis and Body Fluids Case Studies 1 — Questions and Answers
Question 1: A urine dipstick shows 3+ blood but microscopic examination reveals no red blood cells. What is the most likely explanation?
- False positive dipstick
- Hemoglobinuria or myoglobinuria — free hemoglobin or myoglobin in urine causes a positive dipstick without intact RBCs (Correct answer)
- The microscopy was performed incorrectly
- The dipstick is expired
Correct answer: Hemoglobinuria or myoglobinuria — free hemoglobin or myoglobin in urine causes a positive dipstick without intact RBCs
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?
- Viral meningitis
- Bacterial meningitis (Correct answer)
- Normal CSF
- Fungal meningitis
Correct answer: Bacterial meningitis
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?
- Normal urinalysis
- Severe chronic renal disease with tubular damage and stasis (Correct answer)
- Acute urinary tract infection
- Dehydration only
Correct answer: Severe chronic renal disease with tubular damage and stasis
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?
- Congestive heart failure
- Tuberculous pleuritis or malignancy (Correct answer)
- Pulmonary embolism
- Uncomplicated pneumonia
Correct answer: Tuberculous pleuritis or malignancy
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?
- Normal concentrated urine
- Urinary tract infection likely caused by a urease-producing organism (Correct answer)
- Nephrotic syndrome
- Glomerulonephritis
Correct answer: Urinary tract infection likely caused by a urease-producing organism
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.
Question 6: A synovial fluid specimen from an acutely swollen knee joint is examined under compensated polarized light. Needle-shaped crystals showing strong negative birefringence (yellow when parallel to the slow ray compensator) are seen. What is the diagnosis?
- Pseudogout (CPPD)
- Gout (monosodium urate crystals) (Correct answer)
- Septic arthritis
- Osteoarthritis
Correct answer: Gout (monosodium urate crystals)
Needle-shaped crystals with strong negative birefringence (yellow when parallel to the slow ray of the compensator) are monosodium urate (MSU) crystals, diagnostic of gout. CPPD crystals (pseudogout) are rhomboid-shaped and weakly positively birefringent (blue when parallel). Intracellular crystals within neutrophils confirm active crystal-induced inflammation.
MLPAO Urinalysis and Body Fluids Case Studies 1
A urine dipstick shows 3+ blood but microscopic examination reveals no red blood cells.
What is the most likely explanation?