Clinical Microscopy (Urinalysis and Body Fluids)
Clinical Microscopy tests urinalysis and body-fluid analysis: dipstick chemistry, microscopy, cell counts, crystals, casts, and fluid classification. The exam rewards systematic correlation of chemical and microscopic findings.
Core rules
- Dipstick blood detects peroxidase activity from RBCs, hemoglobin, or myoglobin. A positive blood with few RBCs suggests hemoglobinuria or myoglobinuria.
- Leukocyte esterase and nitrite suggest urinary tract infection; nitrite depends on nitrate-reducing organisms and may be negative with frequent voiding.
- Microscopy reports RBCs, WBCs, epithelial cells, casts, crystals, and organisms per high-power field. Squamous epithelial cells indicate contamination.
- Hyaline casts are nonspecific; RBC casts suggest glomerular bleeding; WBC casts suggest pyelonephritis.
- Body fluids are classified as transudate or exudate using protein, LDH, cell count, and clinical context. CSF glucose compares with serum glucose.
Worked example
A midstream urine is cloudy, leukocyte esterase positive, nitrite positive, and microscopy shows 25 WBC/hpf and many bacteria. Interpretation: probable urinary tract infection. Reasoning: positive esterase and nitrite plus pyuria and bacteriuria are concordant. A culture is needed for organism and susceptibility; contamination is less likely because squamous epithelial cells are few.
Traps
Dipstick timing affects results; read at the stated interval. Refrigerated urine can precipitate amorphous crystals. A negative nitrite does not exclude infection. Do not report a fluid as exudate from protein alone; use validated criteria. Sputum and stool are not urine specimens-reject mislabeled containers.