Certified Medical Assistant (CMA AAMA)Procedures, Examinations and DiagnosticsEasy
A physician orders a stat plasma electrolyte panel that requires rapid turnaround. Which evacuated tube additive is most appropriate for this collection to avoid the clotting time needed for serum separation?
- ALithium heparin (green-top)
- BClot activator with no anticoagulant (red-top)
- CSodium citrate (light blue-top)
- DEDTA (lavender-top)
Show answer & explanationAnswer & explanation
Correct answer: A. Lithium heparin (green-top)
Lithium heparin tubes prevent clotting by inactivating thrombin, allowing plasma to be separated immediately by centrifugation without waiting for clot formation, making it ideal for stat chemistry testing.
Why the other options are wrong
- B. Red-top tubes require clotting time before centrifugation, delaying results.
- C. Sodium citrate is used for coagulation studies, not electrolyte panels.
- D. EDTA is used for hematology studies like CBCs, not chemistry panels.
Heparin Tube for Stat Chemistry
Lithium or sodium heparin tubes (green-top) prevent clotting, allowing rapid plasma separation for time-sensitive chemistry testing.
- Heparin inhibits thrombin formation
- Used for stat electrolytes and blood gases
- No clot time needed before centrifugation
Memory trick: Green means go fast—heparin skips the clot wait.