The prothrombin time (PT) is the most commonly used anticoagulant test and was first introduced into use by Dr. Armand Quick and colleagues in 1935.1 The PT is used to evaluate the tissue factor (TF) and common coagulation pathway thus affecting the activity of the coagulation factors II (FII, V (FV), VII (FVII), X (FX), and fibrinogen. This test is also used to measure the effect of warfarin and measures the time in seconds required for clot formation after thromboplastin reagent (a mixture of TF, lipids, and calcium chloride) is added to platelet-poor-plasma (PPP).1 International normalized ratio (INR) is a way of expressing the PT in a standardized way by comparing to a reference value and also ensures that results obtained by various laboratories in different facilities can be compared reliably.2
INR monitoring is required for the patients who are on warfarin, a vitamin K antagonist. The dose of warfarin is adjusted based on INR results so that it remains in the therapeutic range to prevent thrombosis from subtherapeutic INR or hemorrhagic complications from supratherapeutic INR.1
Solaris diagnostics laboratory now offers in-house PT/INR test with turnaround time of less than 1 hour from the time the sample is received in the laboratory.