What is this test?
APTT measures the time needed for clot formation through part of the coagulation system. It can be used to investigate bleeding and, in suitable protocols, to monitor unfractionated heparin.
Why might it be ordered?
- To investigate unexplained bleeding, bruising or an abnormal coagulation screen.
- To monitor unfractionated heparin when the treatment protocol uses APTT.
What sample is needed?
A blood sample is required. The laboratory chooses the correct tube and handles the sample for this test.
How should you prepare?
Report all anticoagulants and the timing of the last dose. Do not stop or adjust treatment without instructions from the responsible clinician.
How should you understand the result?
A prolonged APTT has several possible causes, including medicines, factor deficiencies and inhibitors. A mixing study or factor tests may be needed to clarify it.
Sources and editorial status
This patient-facing text is an editorial draft. It should be approved by a laboratory physician before official publication.