Laboratory Procedures
The Laboratory Procedures domain tests specimen handling, hematology, chemistry, urinalysis, cytology, parasitology, and quality control. The exam favors questions where a result is implausible and you must identify the preanalytical error.
Core rules
- Collect into the correct tube: EDTA for CBC, heparin or serum separator for chemistry, plain red-top for serum, and sodium citrate for coagulation at the correct fill volume.
- Blood smears should be made immediately; EDTA can distort cells over time.
- Run controls and review reference ranges; a single abnormal value must be interpreted with the patient.
- Urinalysis: assess color, turbidity, specific gravity, pH, protein, glucose, ketones, bilirubin, blood, and sediment.
- Cytology samples should be thin, air-dried, and stained; note cellularity, inflammation, and organisms.
Worked example
A CBC shows WBC 12,000/µL and 5 nucleated RBCs per 100 WBCs. Correct the WBC: 12,000 × 100 ÷ (100 + 5) = 11,428/µL. The correction matters because nRBCs are counted as WBCs by many analyzers; a marked nRBC count can falsely raise the WBC.
Traps
Using a clotted EDTA sample, underfilling a citrate tube, delaying smear preparation, and interpreting hemolysis as true hyperkalemia. Also, failing to examine urine sediment. Always compare the result with the patient and the sample quality.