The PT test (scientific name- tissue activated induced coagulation time) has been in clinical practice for over 60 years. The first standardised one-stage PT test was devolved by Dr. Armand Quick in 1932. It has now become the basic coagulation screening test for the diagnosis of acquired and congenital deficiencies of clotting factors in the Extrinsic pathway. The assay was designed to measure a coagulation defect before the introduction of oral anticoagulants, and later adapted for monitoring their dosage. The PT reflects changes in the Extrinsic factors II, VII and X, three of the principle clotting factors depressed by Coumarin drugs, and FV, not reduced by oral anticoagulation. It can also be used to assess the protein synthesis capability of the liver in chronic or acute hepatic disorders. The test depends on the activation of Factor X in the presence of Factor VII by Tissue Factor (TF) and bypassing of the Intrinsic clotting pathway. The speed of the reaction and the responsiveness of the PT to deficiencies of clotting factors depend upon the properties and concentration of the TF as well as on the clotting factor concentrations.
Preparation of patients: Patients should be relaxed pre-venepuncture. Excessive stress and exercise will increase Factor VIII, vWF antigen and fibrinolysis. Veno-occlusion should be avoided.
Precautions: The doctor should check to see if the patient is taking any medications that may affect test results. This precaution is particularly important if the patient is taking Warfarin, because there are a number of medications that can interact with Warfarin to increase or decrease the PT time
