NHA Certified Phlebotomy Technician (CPT)Specimen HandlingMedium
A phlebotomy technician is processing a serum specimen that requires centrifugation. Which of the following indicates that the specimen is NOT ready for centrifugation?
- AThe tube has been inverted 5 times after collection.
- BThe gel separator is clearly visible at the bottom of the tube.
- CThe specimen has been sitting for 30 minutes at room temperature.
- DA fibrin clot is visibly formed at the bottom of the tube.
Show answer & explanationAnswer & explanation
Correct answer: A. The tube has been inverted 5 times after collection.
Serum specimens (e.g., in red or gold top tubes) require a complete clotting time, typically 30 minutes at room temperature, before centrifugation. Inverting a plain serum tube is not part of the standard process, and if it's a tube with clot activator, 5 inversions may not be sufficient for complete activation and clotting.
Why the other options are wrong
- B. The presence of a gel separator is normal for some serum tubes and does not indicate it is not ready for centrifugation, assuming clotting is complete.
- C. 30 minutes at room temperature is a common timeframe for complete clotting of serum specimens, indicating it is ready for centrifugation.
- D. A visibly formed fibrin clot indicates the clotting process is complete, making the specimen ready for centrifugation.
Serum Clotting Time
Serum specimens must be allowed to clot completely before centrifugation to ensure proper separation of serum from blood cells and fibrin.
- Typically 30 minutes at room temperature.
- Insufficient clotting leads to fibrin strands.
- Clot activators shorten time, but still need full activation.
Memory trick: Let it clot, then spin; don't rush the separation within!