Hematology · 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 (s)

Mean normal prothrombin time (s)

International sensitivity index (ISI) (ISI)

Result

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Formula inputs

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

Primary source

Poller L et al. A multicentre randomised clinical trial of a new model of delivery of oral anticoagulant treatment with computerised decision support. J Clin Pathol. DOI: 10.1136/jcp.51.4.299. PMID: 9708184. Scope: INR = (patient prothrombin time / geometric mean normal prothrombin time)^ISI using the international sensitivity index for the thromboplastin reagent. (1998)

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