INR
Standardized prothrombin time ratio.
RESULT
INR
What is INR?
Standardized prothrombin time ratio. INR is intended for use in: Adults.
How to Use the INR Calculator
- Enter Patient PT in sec.
- Enter Mean normal (control) PT in sec.
- Enter ISI (International Sensitivity Index) of the reagent.
- Click Calculate to see your result and interpretation.
Formula & Version
This calculator uses formula version 1.0, last reviewed September 2026.
Clinical Considerations & Limitations
- ISI is specific to the thromboplastin reagent/instrument combination used by the laboratory — using the wrong ISI gives an incorrect INR.
References
- WHO Expert Committee on Biological Standardization, 1983 (INR standardization)
Frequently Asked Questions
What is INR?
Standardized prothrombin time ratio.
Who is INR intended for?
Adults. Always confirm applicability to your specific patient before use.
What are the limitations of INR?
ISI is specific to the thromboplastin reagent/instrument combination used by the laboratory — using the wrong ISI gives an incorrect INR.
What formula or reference does INR use?
WHO Expert Committee on Biological Standardization, 1983 (INR standardization)
Is INR a diagnosis?
No. INR produces a score or estimate to support clinical decision-making — it is not a diagnosis and should be interpreted alongside full clinical judgement.
Medical Disclaimer: Medical calculators are provided for informational and educational purposes only. Results should not be used as a substitute for professional medical advice, diagnosis, or treatment. Always verify results with a qualified healthcare professional.
