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Prothrombin time

Alias: PT/INR (Warfarin)

Discipline: Coagulation

Test information: Prothrombin is a protein made by the liver. Prothrombin helps blood to clot. The "prothrombin time" (PT) is one way of measuring how long it takes blood to form a clot, and it is measured in seconds.
The PT measures the activity of the Extrinsic and common factors of the Coagulation pathway.
It is used alongside the Activated Partial Thromboplastin Time (APTT) as a general screening procedure for clotting abnormalities, liver function assessment and for monitoring patients receiving Warfarin anticoagulant therapy.

Specimen Type(s)
  • Blood;
Other Acceptable Specimen Type(s)
Specimen Container - Adult
  • Light Blue Top BD;
Specimen Container - Paediatric
  • N/A;
  • N/A;
Part of a test profile?
Thrombophilia screen
Volume (min) of sample to be sent to laboratory
Patient Preparation, Sample Handling and Transport
Coagulation samples are volume critical, if a patient is difficult to bleed paediatric tubes (1.3ml) are available on request.
Some patients with a grossly raised Haematocrit (HCT) >0.57 may give erroneous coagulation test results - individual patient adjusted volume coagulation tubes are available on request from the laboratory. Please make a note of any anticoagulants and/or bleeding/bruising symptoms.
Maximum add on time
24 hours
Units and Reference Ranges / Interpretation
Interpretative comments
UKAS number
UKAS accredited test?

If you have any queries about a test or results interpretation please contact us.

Last updated: 03-05-2024