Minus/plus icon
ResourcesExplore the full ACKO experience and make the most of your plan
health plus

INR Calculator

Stay updated on your INR levels with a reliable and user-friendly calculator.

✅Plans starting @ Rs. 20/day* ✅Zero waiting period and out of pocket costs

Zero Waiting period
Waiting period
14,300+ Cashless hospitals
Cashless hospitals
100% Bills covered
Bills covered
health plus

Home / Health Insurance / Calculators / Articles / INR Calculator

The International Normalised Ratio (INR) Calculator is an important tool for medical professionals in order to quickly calculate and monitor patients' coagulation levels. INR is a unit-free ratio that indicates how long it takes blood to clot in comparison to a normal reference sample.

The World Health Organization (WHO) developed and maintains the INR as an internationally acknowledged standard for evaluating blood clotting times. To calculate the INR, medical professionals measure the patient's prothrombin time (PT), the time it takes for blood to clot after tissue factor stimulation, and compare it to that of a normal reference sample. The INR is then calculated from the PT to provide more consistent findings among laboratories that may utilise various methods of analysis or reagents.

In this article, we will go through the basics of INR, its significance, and how to utilise an INR Calculator to calculate the proper dosage of blood-thinning medicine for patients.

What is an INR Calculator?
Jump Tag Icon

An International Normalised Ratio (INR) Calculator is a tool used to compute the ratio of a patient's blood sample's prothrombin time (PT) to a standardised PT. The time it takes for a patient's blood to clot is measured by the PT, and the INR Calculator accounts for variations in the sensitivity of PT test reagents used by various laboratories. The INR is a standardised test of blood clotting that may be utilised to track patients who are taking blood thinners like warfarin.

The INR Calculator needs the PT value of the patient, the mean normal PT value of the laboratory, and the International Sensitivity Index (ISI) value for the PT reagent used. Once these variables have been put into the calculator, the patient's INR value will be shown, which may be used to monitor and modify their medicine doses. 

The INR Calculator can also be used to inquire about blood clotting disorders such as haemophilia or Von Willebrand's disease. It may also be utilised to manage patients with liver or renal problems who may have impaired clotting function.

The calculator provides a number of options designed to facilitate exact and effective calculations, including patient gender, age, weight, and dosages of medications. It may also account for various reagents that may be used to measure PT. 

This measurement is used by physicians to determine the most effective drug dosages, assess the treatment efficacy, and limit the risk of bleeding or clotting issues. The INR Calculator offers an instant and accurate technique for calculating INR and making proper clinical decisions, leading to better results for patients.

What does the INR result mean?
Jump Tag Icon

If your INR is high, the blood takes longer to clot. An elevated INR may indicate an increased risk of bleeding, whereas a low INR may indicate the probability of thromboembolism issues.

A PT INR test is an easy and effective method of regulating treatment for individuals who have atrial fibrillation, artificial heart valves, thromboembolism, stroke, or any peripheral artery disease.

Following are the different levels of INR that represent various conditions in an individual.

Other potential causes of elevated INR may include the following.

How is the INR Calculator used?
Jump Tag Icon

The INR calculator requires the following types of information.

1. The PT or prothrombin time of the patient in seconds.

2. The controlled prothrombin time of the standard sample utilised in your local diagnostic centre in seconds.

3. The ISI (International Sensitivity Index) value found by a specified manufacturer. It assesses the sensitivity of the tissue factor utilised in the PT analysis.

How to calculate INR using PT?
Jump Tag Icon

The INR Calculator uses the following formula to get the INR.

INR = (Patient′s PT/Control PT)*ISI


Patient′s PT = Patients measured PT in seconds

Control PT = Laboratory’s geometric mean value for normal patients in seconds

ISI = International Sensitivity Index

For example,

A patient on oral anticoagulant had a PT of 64 seconds

A normal plasma has a prothrombin time of 22 seconds

The ISI of thromboplastin is 0.93. Substituting this amount into the above formula yields the following INR.

INR = (64/22)*0.93 = 2.7 INR

This is a 2.7 times increase in coagulation time over the normal range. The higher the INR, the longer the patient's coagulation time.

The values of the ISI typically fall between 0.9 and 1.7. Both control PT and ISI are impacted by the analytical method used and should be well-recognized and widely spread by your local laboratory.

Frequently Asked Questions (FAQs)
Jump Tag Icon

Here are some FAQs about the INR Calculator.


How is the INR calculated?

Here’s the formula:

INR = (Patient′s PT/Control PT)ISI


Patient′s PT = Patients measured PT in seconds

Control PT = Laboratory’s geometric mean value for normal patients in seconds

ISI = International Sensitivity Index

What should be the normal range of INR?

INR of 1.1 or less is known to be normal in healthy adults. 

What is the INR ratio?

The international normalised ratio (INR) is a recommended test for people with vitamin K antagonists (VKA). It can also be used to determine a patient's risk of bleeding or coagulation status. Because INR varies between people, patients using oral anticoagulants must monitor their INR in order to adjust their VKA dosage.

What will happen if the INR is high?

If your INR is excessively high, you are more likely to have bleeding, which could be fatal. Fortunately, there are drugs that can reverse anticoagulation and help stop the bleeding.


Disclaimer: The content on this page is generic and shared only for informational and explanatory purposes. Please consult a doctor before making any health-related decisions.