Clinical Laboratory Techniques and Procedures
What this domain tests
This domain tests pre-analytical, analytical, and post-analytical steps: patient preparation, sample collection, anticoagulants, transport, centrifugation, staining, hematology, biochemistry, and urinalysis.
Core rules
- Identify the patient and label the sample at collection. Use the correct tube and anticoagulant: EDTA for CBC, citrate for coagulation, plain or gel tube for many biochemistry tests.
- Avoid hemolysis, delay, and improper temperature. Clotted or hemolyzed samples can invalidate results.
- Centrifuge balanced tubes at the specified speed and time. Do not decant forcibly.
- For manual WBC counting, use a hemocytometer, lyse red cells, and count the specified squares. WBC/µL = cells counted × dilution ÷ volume counted in µL.
- Urinalysis includes physical, chemical, and microscopic examination. Read dipsticks at the stated time; do not read after the window.
- A good blood smear is thin, feathered, and not too thick at the tail.
Worked example
In a manual WBC count, 120 cells are counted in four large squares. The dilution is 1:20. Each large square is 1 mm² and the chamber depth is 0.1 mm, so the counted volume is 4 × 1 × 0.1 = 0.4 mm³ = 0.4 µL. WBC = 120 × 20 ÷ 0.4 = 6000/µL. The reasoning is that dilution multiplies the counted cells, while volume converts the count to cells per µL.
Traps
Do not use an EDTA tube for a clotted CBC. Do not shake vigorously. Do not report a result from a mislabelled sample. Do not count cells outside the ruled area. Do not read dipsticks late.