A phlebotomy technician is processing a serum specimen that requires centrifugation. Which of the following situations would most likely lead to specimen rejection due to incomplete clotting?
- ACentrifuging the specimen 5 minutes after collection.
- BCentrifuging the specimen 60 minutes after collection.
- CStoring the specimen in a tube with a gel separator.
- DMixing the tube vigorously immediately after collection.
Show answer & explanationAnswer & explanation
Correct answer: A. Centrifuging the specimen 5 minutes after collection.
Serum tubes (e.g., red-top or SST) require a specific clotting time, typically 30-60 minutes at room temperature, before centrifugation. Centrifuging too early (e.g., 5 minutes) will result in incomplete clotting, leading to fibrin strands in the serum and potential re-clotting, which can interfere with testing and cause instrument errors.
Why the other options are wrong
- B. Centrifuging after 60 minutes allows sufficient time for clotting, which is generally appropriate for serum tubes.
- C. Storing the specimen in a tube with a gel separator is appropriate for serum separation after clotting and centrifugation; it does not cause incomplete clotting.
- D. Vigorous mixing can cause hemolysis, but it does not directly cause incomplete clotting; in fact, gentle inversions help activate clot formation when using clot activators.
Incomplete Clotting
Incomplete clotting in serum specimens occurs when the blood is centrifuged before sufficient time has passed for a solid clot to form. This results in fibrin strands remaining in the serum, which can interfere with laboratory testing and instrumentation.
- Common cause: centrifuging too soon.
- Requires 20-60 minutes clotting time for serum tubes.
- Results in fibrin strands, re-clotting.
- Causes specimen rejection and need for recollection.
Memory trick: Let the blood clot, don't spin it hot, or the serum will be a knot.