MLPAO Urinalysis and Body Fluids Case Studies Flashcards

A urine specimen from a child has a positive dipstick for blood and protein. Microscopy shows RBC casts and dysmorphic red blood cells. Serum complement C3 is low. What diagnosis should be suspected?

Answer: Post-streptococcal glomerulonephritis

RBC casts (proving glomerular origin of hematuria), dysmorphic RBCs, proteinuria, and low serum complement (C3 consumption via the alternative pathway) in a child are classic for post-streptococcal glomerulonephritis. This immune-complex mediated disease typically follows a group A streptococcal pharyngitis or skin infection by 1-3 weeks. ASO titer and anti-DNase B confirm recent streptococcal infection.

A CSF specimen from an immunocompromised patient shows 50 WBC/µL with lymphocyte predominance, elevated protein, and low glucose. India ink preparation shows encapsulated yeast. What is the diagnosis?

Answer: Cryptococcal meningitis

Encapsulated yeast on India ink preparation in CSF from an immunocompromised patient (HIV/AIDS, transplant recipients) is diagnostic of cryptococcal meningitis caused by Cryptococcus neoformans. The CSF profile (lymphocytic pleocytosis, elevated protein, low glucose) is similar to TB meningitis. Cryptococcal antigen (CrAg) testing in CSF and serum is more sensitive than India ink.

A urine sample from a patient on the antibiotic nitrofurantoin shows a brown/dark colour. The dipstick is negative for blood. What explains the colour?

Answer: Drug-induced colour change — nitrofurantoin metabolites produce brown/rust-coloured urine as a known harmless side effect

Several medications cause distinctive urine colour changes: nitrofurantoin (brown/rust), rifampin (red-orange), phenazopyridine (bright orange), and metronidazole (dark/red-brown). These are harmless metabolite effects. The negative blood dipstick rules out hematuria. Patient medication history is essential when investigating abnormal urine colour.

A pleural fluid specimen has an amylase level of 1200 U/L (serum amylase 80 U/L) and a pH of 6.0. What conditions should be considered?

Answer: Esophageal rupture (salivary amylase) or pancreatic pleural effusion (pancreatic amylase); the very low pH supports esophageal rupture

Markedly elevated pleural fluid amylase (>3× serum or >upper limit of serum normal) occurs in esophageal rupture (salivary amylase type) and pancreatic disease (pancreatic amylase type). A pH of 6.0 is very low and strongly suggests esophageal rupture (gastric acid contamination). Amylase isoenzyme analysis differentiates salivary from pancreatic origin. Esophageal rupture is a surgical emergency.

A routine urinalysis shows numerous squamous epithelial cells, a few WBCs, and some bacteria. The dipstick shows trace leukocyte esterase and negative nitrite. How should this be interpreted?

Answer: Likely contamination from vaginal/perineal source — squamous epithelial cells indicate improper collection; repeat with proper midstream clean-catch technique

Numerous squamous epithelial cells indicate contamination from the vaginal/urethral area, suggesting an improperly collected specimen. The few WBCs and bacteria may be from the contaminating source rather than from a true UTI. A repeat specimen with proper midstream clean-catch technique and appropriate patient instruction should be requested before diagnosing UTI.

A peritoneal fluid analysis from an ascites tap shows WBC 800/µL with 70% neutrophils, total protein 12 g/L, and a SAAG of 14 g/L. What does this indicate?

Answer: Spontaneous bacterial peritonitis (SBP) in a patient with portal hypertension

The high SAAG (14 g/L) confirms portal hypertension (cirrhotic ascites). The PMN count >250/µL (800 × 70% = 560 PMNs/µL) meets the diagnostic criteria for SBP. SBP occurs in cirrhotic patients when bacteria translocate from the gut. Low protein ascites (<10 g/L) is a risk factor for SBP. Treatment is empiric IV ceftriaxone or cefotaxime.