Certified Medical Assistant (CMA AAMA)Procedures, Examinations and DiagnosticsMedium
A medical assistant collects a red-top serum tube for a chemistry test. What is the primary reason the tube must sit for a specified clotting time before centrifugation?
- ATo allow white blood cells to settle before analysis
- BTo allow complete clot formation so serum can properly separate from the clot
- CTo prevent hemolysis from occurring during transport
- DTo allow the anticoagulant to fully bind with the blood cells
Show answer & explanationAnswer & explanation
Correct answer: B. To allow complete clot formation so serum can properly separate from the clot
Red-top tubes contain no anticoagulant, so the blood must be allowed to fully clot (typically 30-60 minutes) before centrifugation; centrifuging too early can result in incomplete clot formation, causing fibrin strands to appear in the serum and interfering with testing.
Why the other options are wrong
- A. White blood cell settling is not the purpose of the clotting period.
- C. Clotting time does not specifically prevent hemolysis; proper handling technique does.
- D. Red-top tubes do not contain anticoagulant, so this is incorrect.
Serum Clotting Time Before Centrifugation
Red-top (serum) tubes must sit for a specified clotting time, typically 30-60 minutes, before centrifugation to allow complete clot formation and proper serum separation.
- Red-top tubes lack anticoagulant
- Clotting time ensures fibrin doesn't contaminate serum
- Premature centrifugation can cause fibrin strands in serum
Memory trick: 'Let it clot before you spin, or fibrin strands will do you in'