The formula to calculate the International Normalized Ratio (INR) is:
\[ INR = \left(\frac{PT_{patient}}{PT_{normal}}\right)^{ISI} \]
Where:
Let's say the patient's prothrombin time (\( PT_{patient} \)) is 15 seconds, the mean normal prothrombin time (\( PT_{normal} \)) is 12 seconds, and the International Sensitivity Index (\( ISI \)) is 1.1. Using the formula:
\[ INR = \left(\frac{15}{12}\right)^{1.1} \]
We get:
\[ INR ≈ 1.28 \]
So, the International Normalized Ratio (\( INR \)) is approximately 1.28.
The International Normalized Ratio (INR) is a standardized number that’s calculated in the laboratory. It measures how long it takes for blood to form a clot. The INR is used to monitor patients who are on anticoagulant medications, such as warfarin, to ensure that their blood is clotting within a safe and effective range. The INR is particularly useful because it standardizes the results of prothrombin time tests, regardless of the testing method or location, making it easier to compare results across different laboratories and settings.
