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.
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%