Activated Partial Thromboplastin Time Test – Reference Range

  • The reference range of the aPTT is 30-40 seconds.
  • The reference range of the PTT is 60-70 seconds.

Critical values that should prompt a clinical alert are as follows:

  • aPTT: More than 70 seconds (signifies spontaneous bleeding)
  • PTT: More than 100 seconds (signifies spontaneous bleeding)

PTT results are typically reported in seconds. A PTT result that falls within a laboratory’s reference interval usually indicates normal clotting function.

However, mild to moderate deficiencies of a single coagulation factor may be present.

The PTT may not be prolonged until the factor levels have decreased to 30% to 40% of normal. A prolonged PTT means that clotting is taking longer to occur than normal and may be due to a variety of causes. Coagulation factor deficiencies may be acquired or inherited.

* The Content is not intended to be a substitute for professional medical advice, diagnosis, or treatment. Always seek the advice of your physician or other qualified health provider with any questions you may have regarding a medical condition.