Coagulation
INR / Prothrombin time
Extrinsic and common pathway; standardised across labs as INR for warfarin monitoring.
Sample
Citrated plasma
Clinical reference range
0.8 to 1.2
Untreated
Conv: 0.8–1.2
Biology
What it measures
Tissue factor + factor VII initiates the cascade. INR = (patient PT/control PT)^ISI.
Clinical use
Why we order it
Warfarin dosing, liver synthetic function, DIC.
Differential
Causes of abnormal values
Causes of HIGH
- ↑Warfarin
- ↑Liver failure
- ↑Vitamin K deficiency
- ↑DIC
Related