A prothrombin time (PT) test measures how long it takes for a clot to form in a blood sample. An INR (international normalised ratio) is a type of calculation based on PT test results. Prothrombin is a protein made by the liver. It is one of several substances known as clotting (coagulation) factors.

SPECIMEN: 3 mL whole blood in 1 Blue Top (Sodium Citrate) tube. Mix thoroughly by inversion. Transport to Lab within 4 hours. If this is not possible, make PPP within 1 hour of collection as follows: Centrifuge sample at 3600 rpm for 15 min. & transfer supernatant to a clean plastic tube. Centrifuge this supernatant again at 3600 rpm for 15 min. & finally transfer the supernatant (PPP) to 1 labelled clean plastic screw capped vial. FREEZE IMMEDIATELY. Ship frozen. DO NOT THAW.
STABILITY: Room: 4 hrs; Refrigerated: 4 hrs; Frozen: 2 weeks
REPORT: Daily
USAGE: Prothrombin time measures the time it takes for plasma to clot when exposed to tissue factor. Since PT comprises reactions of coagulation that occurs in tissue injury & common pathways of coagulation, deficiencies in the activity of Factors II, V, VII, X or fibrinogen may prolong the PT. INR standardises the reporting of PT values in Warfarin anticoagulated patients.