Clinical Laboratory Procedures
This domain tests sample collection, tube selection, processing, CBC and chemistry interpretation, urinalysis, and quality control.
Core rules
- EDTA (lavender) for CBC; serum separator or heparin for chemistry; citrate (light blue) for coagulation. Fill citrate tubes to the line because underfilling alters results.
- Analyze urine fresh or refrigerate; cystocentesis is preferred for culture. Measure USG before refrigeration if possible.
- Hemolysis, lipemia, and delayed processing alter results. Run controls and record QC.
- Calculate absolute counts from percentages: absolute = total WBC × percentage.
Worked example
A CBC shows WBC 12,000/µL with 80% neutrophils. The absolute neutrophil count is 12,000 × 0.80 = 9,600/µL. The technician compares this with the laboratory reference interval and reviews the smear for toxic change. The reasoning: percentages alone can mislead; absolute counts show whether neutropenia or neutrophilia is real.
Traps
Using a serum tube for a CBC, underfilling a citrate tube, delaying urine analysis, and ignoring lipemia are common. EDTA can cause platelet clumping, so review the smear before calling thrombocytopenia.