Evaluate an isolated prolonged PT or for evaluation when both the APTT and PT are prolonged and to assess factor V activity level.
Ideally the patient should not be on anticoagulant therapy. Avoid warfarin (Coumadin®) therapy for two weeks prior to the test and heparin, direct Xa, and thrombin inhibitor therapies for about three days prior to testing.
To avoid delays in turnaround time when requesting multiple tests on frozen samples, submit a separate frozen aliquot for each test requested.
Factor V activity is determined utilizing a prothrombin time (PT)-based one-stage clotting time assay. Factor V-depleted plasma is used as the substrate, and the clotting time with the patient plasma is compared to the clotting time of normal pooled plasma.
70 - 150%