Fasting Required: No Specimen: Blood Results: 1-2 Business Days Description: The Prothrombin time (PT) test is most often used to check how well anti-coagulant or “blood-thinning” drugs are working. Anti-coagulant drugs help prevent the formation of blood clots. This is particularly important in people who have had a heart attack or other problems with their veins. The drug’s effectiveness can be determined by how much it prolongs the prothrombin-to-thrombin conversion time. Methodology: Photo-optical Clot Detection Limitations: Expected impact by therapeutic levels (potential interference depends upon drug concentration): Warfarin: prolonged; Heparin (UFH or LMWH): little to no effect (reagent contains a heparin neutralizer); Dabigatran or Argatroban (Thrombin Inhibitors): normal to prolonged; Rivaroxaban or Apixaban (Factor Xa Inhibitors): prolonged. Clinical Significance: Screening test for abnormalities of coagulation factors that are involved in the extrinsic pathway. Also used to monitor effects of Warfarin therapy and to study patients with hereditary and acquired clotting disorders. Alternative Name(s): PT