Specimen Collection, Handling, and Processing
Core concepts
Most laboratory errors originate before analysis. Candidates must know patient preparation, collection timing, tube selection and order of draw, anticoagulants, and the effects of hemolysis, lipemia, and icterus. Understand additive tubes (EDTA, citrate, heparin, oxalate/fluoride) and which tests each supports. Know that citrate tubes require correct fill volume to maintain the 9:1 blood-to-anticoagulant ratio, and that EDTA binds calcium.
Handling and processing
Recall stability, transport temperature, light protection, and time limits. Centrifugation speed and time affect separation quality. Know serum vs plasma differences and why some analytes require immediate separation. Special handling includes chilling, warming, and protecting from light.
Traps in questions
- Order-of-draw errors, especially drawing citrate after EDTA contamination concerns.
- Short-draw citrate tubes causing falsely prolonged clotting times.
- Assuming hemolysis affects only potassium (it also affects LDH, AST, and others).
- Confusing fasting requirements with random collection.
Worked rule of thumb
Use the order of draw mnemonic: blood culture, then sodium citrate, then serum tube with or without clot activator, then heparin, then EDTA, then oxalate/fluoride. When a question describes a short-filled citrate tube, the correct action is rejection and recollection, not correction.
Study guidance
For every analyte mentioned in practice questions, ask: what tube, what handling, what stability, and what interference? That four-part framework resolves most pre-analytical items.