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INR

International Normalised Ratio PT-INR
Sodium citrate (blue top) Ratio (dimensionless)

About this test

Standardised ratio derived from the PT using the International Sensitivity Index (ISI) to allow inter-laboratory comparison. The standard metric for monitoring warfarin therapy.

Reference Ranges

Sex Age Range Notes
All ≥ 18 yrs 0.8 – 1.2 Normal coagulation. Therapeutic ranges: AF/DVT/PE (target 2.5; range 2–3); mechanical heart valve (target 3.0; range 2.5–3.5)

Clinical Interpretation

Low / Decreased
INR <2 (on warfarin) — subtherapeutic, thrombotic risk.
High / Increased
INR >4 — increased haemorrhagic risk. INR >8 — high major bleed risk; consider vitamin K. Causes: warfarin over-anticoagulation, liver failure, DIC.
Specimen
Sodium citrate (blue top)
Reporting Unit
Ratio (dimensionless)
Category
🩹 Coagulation

⚠ Clinical Note
Reference ranges are indicative. Always interpret results in the context of the individual patient and local laboratory reference intervals, which may vary.