The international normalized ratio (INR) is the ratio of the patient’s prothrombin time to the normal prothrombin time, which is the cube of the ISI (ISI: International Sensitivity Index, calibrated by the manufacturer at the time of the reagent), and is a way to calibrate the difference in prothrombin time measurement values due to the difference in coagulation function reagents. The same sample collected in different laboratories and tested with different ISI reagents can have very different results in blood prothrombin time values, but the measured INR value is the same, making the results comparable. Internationally, INR is used to detect the dosage of oral anticoagulants, which is a good expression form.

Sample collection

1. Tie an elastic band around the arm temporarily to block the venous blood flow, which is beneficial for the venipuncture procedure.

2. Use medical alcohol to disinfect the needle, insert the needle into the vein, connect a test tube to the needle, and collect the blood.

3. After the blood is collected, remove the elastic band from the arm.

4. After removing the needle, apply a piece of gauze or cotton ball to compress the puncture site.

5. There is no specific regulation on whether it should be taken on an empty stomach.

Clinical manifestations

Measuring INR is the preferred method for detecting the dosage and efficacy of warfarin. When using warfarin for anticoagulation treatment, it is generally required that INR be maintained at 2.0～3.0, which can ensure the effectiveness of the treatment and keep the risk of bleeding at a low level. For those with a higher risk of bleeding, INR can be considered to be maintained at 1.5～2.0, but the efficacy may be slightly reduced. INR testing should start 1～2 days after the patient begins to take warfarin, initially once every 2～3 days, and adjust the dosage of warfarin based on the INR results. If two consecutive INR tests are within the therapeutic range, it can be changed to once a week. For those who have a stable warfarin dosage, INR can be tested once every 4 weeks.

Standard value reference range

The INR standard value range is 0.8～1.2. The World Health Organization requires the use of oral anticoagulants for the treatment of deep vein thrombosis, and the allowable range of INR is 2.0～3.0.

Common problems

1. When performing venipuncture, the tension of the elastic band should be appropriate.

2. The disinfection of the blood collection site and the fingers of the collector must be carried out according to the regulations.

3. Blood collection needles should not be reused multiple times.