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Another Challenging PTT Question

Here is an interesting message from Twyla Bader at Peace Health:

1. What is a reasonable lower limit for reporting an APTT? We have Diagnostica Stago Compacts, our normal range is 23.0 – 35.0 seconds and our reportable range currently is 4.0 – 200.0 seconds. I don’t believe I have ever encountered a sample with a value less than 19.0 that wasn’t a clotted sample. 
2. While investigating an APTT result reported the previous evening from our lab of <4.0 seconds I discoverd the specimen contained fibrin and also that the sample had been collected minutes before the patient expired. Is it possible that this plasma had been activated in vivo, therefore an accurate result?

Hi, Twyla, thank you for your question.

About your first question, I would append a comment to any PTT result shorter than the lower limit of the reference range, as it indicates partial activation of the coagulation mechanism. I’d first inspect the specimen to insure there wasn’t a collection error, perhaps even repeat the collection if I was unsure. Sometimes factor VIII can be elevated enough to slightly shorten the PTT, though it wouldn’t account for extremely short values.

In the case of the recently expired patient, the < 4.0 second indication was a correct response to the fibrin. It is likely the patient was a victim of in vivo coagulation activation, perhaps acute DIC, I’m not sure I would call that an accurate result, though. No matter the reason, it is impossible to gain accurate lab test results from a specimen that is activated and partially clotted. I’d advocate for a comment to the physician explaining the probabilities, though at this point it is academic. Geo

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