Haematology · Internal Medicine

International Normalized Ratio (INR) from Prothrombin Time calculator

Enter the published formula inputs below to calculate and interpret this score.

Clinical inputs

Patient prothrombin time

Allowed range: 8–120 s

Mean normal prothrombin time

Allowed range: 8–20 s

International sensitivity index (ISI)

ISI

Allowed range: 0.5–2.5 ISI

Result

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Clinical inputs

Patient prothrombin time (s)Accepted range: 8 to 120
Mean normal prothrombin time (s)Accepted range: 8 to 20
International sensitivity index (ISI)Accepted range: 0.5 to 2.5

Primary source

Poller L et al. European Concerted Action on Anticoagulation. A multicentre calibration study of WHO international reference preparations for thromboplastin. J Clin Pathol. 2005;58:667-669. DOI: 10.1136/jcp.2004.019810. PMID: 15917425. Scope: INR = (patient prothrombin time / mean normal prothrombin time)^ISI using the WHO international sensitivity index for the thromboplastin reagent. (2005)

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