If in the blood, according to the blood tests, the APTT is 233 (norm is 150), does it mean that there was an error during the test, or it may actually be true?

  • 3
    The result of an APTT test is measured in seconds - do you mean that the blood never clotted?
    – YviDe
    Mar 14, 2016 at 9:28
  • 2
    To make this clearer: there is no APTT in blood that can be missing - the APTT measures how many seconds it takes for blood to clot.
    – YviDe
    Mar 14, 2016 at 13:20
  • 2
    "Never clotted" on assays I've seen reads out as ">150 s". Labs may differ on the upper limit, but if it's run and it doesn't clot, it should read "> x seconds" (as YviDe said, it can't really be "missing"). It is, however, possible to run a PT/INR and no (A)PTT -- do you just mean there was a blank space on the result sheet?
    – Susan
    Mar 14, 2016 at 16:34
  • 3
    The above comments were flagged for being answers. I don't believe they are answers, as they are trying to determine what was assessed, and giving reasons why there should be something on the test related to APTT.
    – JohnP
    Mar 14, 2016 at 20:54
  • 1
    You can always edit your question to clarify the confusion (although you've already got a proper answer). For future reference, units are very important for lab tests - if there are any you should include them. In this case if the result was measured in seconds, you can edit your question to state that.
    – Lucky
    Mar 15, 2016 at 11:39

1 Answer 1


The Activated Partial Thromboplastin Time is a test measuring clotting factors, not a level of clotting factors in your blood. It is most often used to monitor the effects of heparin therapy (an anticoagulant.)

Because different labs use different tests, the "normal" results may vary. The results are reported in seconds; for example the Mayo Clinic reports

the therapeutic APTT range to be approximately 70 to 120 seconds.

There is a limit for how long the reaction will be observed (if the blood doesn't clot in a reasonable amount of time, people need to report that as "negative at (upper threshold in seconds for institution.)"

You might want to review the lab report.

Activated Partial Thromboplastin Time (APTT), Plasma
Recommendations for appropriate activated partial thromboplastin time reagent selection and utilization.

  • Thank you very much for the answer, now I understand. My relative has a problem with clotting factor 8 - (233, norm is 150).
    – Rumata
    Mar 15, 2016 at 11:34

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.