Clinical Laboratory Procedures: sample handling and interpretation
Clinical Laboratory Procedures and Diagnostics
This domain tests specimen collection and handling, in-house analyzers, and interpretation of CBC, chemistry, urinalysis, cytology, and coagulation results.
Core rules and concepts
- Tube selection: EDTA (lavender) for CBC - fill to the line and mix by inversion; serum separator (red/tiger) for chemistry; sodium citrate (light blue) for coagulation, filled to 90% capacity because the ratio is 9:1 blood to citrate; heparin (green) for selected chemistries.
- Order of draw to avoid carryover: blood culture, citrate, serum, heparin, EDTA.
- PCV/TS: dog PCV 37–55%, TS 6.0–7.5 g/dL; cat PCV 30–45%. PCV by centrifugation, TS by refractometer.
- Urinalysis: cystocentesis preferred; dipstick then sediment. USG roughly 1.015–1.045 in dogs, 1.035–1.060 in cats.
- Cytology: thin smears, air-dried, Diff-Quik stained; do not refrigerate slides.
Worked example
A 10-year-old dog has pale gums. PCV 19%, TS 4.2 g/dL. Low PCV with low protein points toward blood loss or protein-losing disease rather than dilution. Examine the smear for polychromasia and nucleated RBCs - regeneration takes 3–5 days, so an acute bleed may not yet show it. Pair with a coagulation panel and imaging rather than concluding "non-regenerative anemia" on day one.
Traps
Underfilled citrate tubes falsely prolong PT/PTT. Hemolysis falsely raises potassium and LDH. Lipemia interferes with chemistry. Never submit EDTA blood for chemistry - EDTA chelates calcium and contaminates results. Refrigerated slides distort cells.