INR (International Normalised Ratio)

Standardised measure of clotting time — essential for anticoagulation monitoring.

What it is

INR standardises prothrombin time across different laboratories and reagents, allowing comparison of results between centres. It is derived from the PT result and a calibration factor specific to the reagent used.

Why it matters

INR is the primary monitoring metric for patients on warfarin anticoagulation. Cancer patients frequently develop blood clots (VTE) and may require anticoagulation. An INR outside the therapeutic range (2.0–3.0 for most indications) increases either clotting risk (if low) or bleeding risk (if high).

How to test

Coagulation panel blood test.

This information is for educational purposes only. Always discuss testing and interpretation of results with your care team.

Optimal range

Below 1.2

normal (not on anticoagulation)

Above 3.0

elevated — bleeding risk if on anticoagulation

How often

Monthly if on anticoagulation. Each comprehensive panel if not.