Laboratory Procedures and Diagnostics
What the exam tests
Laboratory Procedures and Diagnostics covers sample collection and handling, CBC and chemistry interpretation, urinalysis, cytology, and quality control.
Core rules
- Use the correct tube: EDTA for hematology, lithium heparin or serum for chemistry, sterile container for urine culture.
- Mix by inversion, not shaking; process promptly or refrigerate as appropriate.
- CBC includes PCV, total protein, WBC count and differential, and platelet estimate.
- Urinalysis: specific gravity, dipstick chemistry, and sediment exam; interpret together, not in isolation.
- Recognize preanalytical artifacts: hemolysis, lipemia, icterus, clotted samples, and storage delay.
Worked example
A WBC count is 30,000/µL with 20 nucleated RBCs per 100 WBCs. Corrected WBC = 30,000 × [100 ÷ (100 + 20)] = 30,000 × 0.833 = 25,000/µL. The nucleated RBCs inflate the automated count, so correcting prevents overestimation of inflammation or leukemia.
Traps
- Reading a platelet count from a clumped EDTA sample and calling thrombocytopenia.
- Ignoring hemolysis, which falsely raises potassium and can alter enzyme results.
- Interpreting urine dipstick protein without specific gravity or sediment.
- Using an expired reagent or failing to run daily controls.
- Calling a slide normal without examining the feathered edge for platelets and organisms.