The prothrombin time (PT) is the screening test for the reactions of the extrinsic pathway. PT is most commonly used for monitoring oral anticoagulant therapy and for performing factor assays for the extrinsic system. A prolonged PT value is most often indicative of a decreased level of one or more of the factors in the extrinsic or common pathways of coagulation. An increased PT usually indicates defective or decreased synthesis of vitamin K-dependent clotting factors. The PT assay is also sensitive to decreases in factor V and fibrinogen, which may accompany end-stage liver disease or, disseminated intravascular coagulation (DIC).
The 9:1 blood/citrate ratio must be kept constant. Adjustments for the amount of anticoagulant should be made when the hematocrit is abnormal (above 55%). Mix immediately to prevent clotting.
Collection Instructions
Send whole blood sample(s) at room temperature as soon as possible. If specimens cannot be shipped immediately, centrifuge and separate plasma within 1 hour of collection, send frozen plasma on dry ice
Fridge: N/A
Room Temperature: 24 hours Freezer: - 20 °C 2 weeks - 70 °C 6 months