Laboratory Procedures
What this domain tests
Laboratory procedures covers sample collection, handling, CBC, chemistry, urinalysis, cytology, and quality control. The exam tests whether you can recognize preanalytical errors and interpret basic results.
Core rules
- EDTA whole blood for CBC; serum or lithium heparin for chemistry; avoid EDTA for chemistry because it can falsely increase potassium.
- Label tubes, fill to the correct volume, mix by inversion, and process promptly.
- Common artifacts: hemolysis falsely increases potassium, ALT, and AST; lipemia causes interference; delayed separation alters results; platelet clumping falsely lowers counts.
- CBC includes PCV, total protein, WBC, RBC, platelets, and blood smear review.
- Urinalysis includes specific gravity, dipstick, and sediment; interpret with hydration status.
- Cytology uses fine-needle aspirate or impression smear; handle slides gently.
- Run daily controls and log calibration.
Worked example
A CBC shows WBC 12,000/µL and 10 nucleated RBCs per 100 WBC. Correct for nRBCs: corrected WBC = 12,000 × 100/(100 + 10) = 10,909/µL, about 10,900/µL. The nRBCs indicate marrow response or disease; do not report the raw count as the leukocyte count.
Traps that cost marks
Using an EDTA tube for chemistry; underfilling citrate tubes; reading a lipemic sample as valid; ignoring platelet clumps; delaying smear review; not recording sample time.