Clinical Pathology: Urine, Stool and Body Fluid Analysis
What this domain tests
This section covers physical, chemical and microscopic examination of urine, stool and body fluids, with emphasis on specimen collection and safe interpretation.
Core rules
- Collect a clean-catch midstream urine in a sterile container; examine within 1-2 hours or refrigerate. A first-morning sample is best for protein and microscopy.
- Dipstick protein mainly detects albumin; it can miss Bence Jones protein. Glucose and blood pads can be affected by ascorbic acid, giving false negatives.
- Microscopy reports red cells, white cells, epithelial cells, casts, crystals and organisms per high-power field.
- Stool examination includes colour, consistency, occult blood, ova, cysts and parasites. A fresh sample is essential for motile trophozoites.
- For CSF and serous fluids, record appearance, cell count, protein, glucose and microbiology. A traumatic tap shows decreasing red cells in successive tubes.
- Distinguish transudate from exudate using protein and cell content; exudates are protein-rich and cellular.
Worked example
A urine dipstick is positive for nitrite and leukocyte esterase, and microscopy shows many white cells and bacteria. Reasoning: this pattern suggests a urinary tract infection. Send the sample for culture and sensitivity before antibiotics; do not diagnose from the dipstick alone.
Traps
- Reading a urine sample left at room temperature for hours.
- Assuming dipstick protein detects all proteins.
- Confusing squamous epithelial cells with white cells.
- Calling a traumatic tap a true hemorrhage.