PROTHROMBIN TIME- PT
Pre-test preparation or requirements
• Sample can be drawn at any time. No fasting or special preparation required.
• Sample taken in Citrated vial should be immediately centrifuged and transfer plasma to aliquot.
Significance of test
1)The prothrombin time is the time it takes plasma to clot after addition of tissue factor (obtained from animals). This measures the quality of the extrinsic pathway (as well as the common pathway) of coagulation.
2)The prothrombin time (PT) and its derived measures of prothrombin ratio (PR) and international normalized ratio (INR) are measures of the extrinsic pathway of coagulation.
3)They are used to determine the clotting tendency of blood, in the measure of warfarin dosage, liver damage, and vitamin K status. The speed of the extrinsic pathway is greatly affected by levels of factor VII in the body.
4) Factor VII has a short half-life and its synthesis requires vitamin K. The prothrombin time can be prolonged as a result of deficiencies in vitamin K, which can be caused by warfarin, malabsorption, or lack of intestinal colonization by bacteria (such as in newborns).
5) In addition, poor factor VII synthesis (due to liver disease) or increased consumption (in disseminated intravascular coagulation) may prolong the PT.