If you are not taking blood thinning medicines, such as warfarin, the normal range for your PT results is: 11 to 13.5 seconds. Normal Results Most of the time, results are given as what is called INR (international normalized ratio). Not only does warfarin exhibit a narrow therapeutic index, but there can be 10 to 20-fold differences in the warfarin dose required to achieve target INR. Does warfarin have a wide therapeutic range? A usual dose requirement is between 5 to 7.5 mg. Expressed in terms of the INR, the range is between 2.0 and 3.0. Therapeutic levels are generally between 1 1/2 and 2 times normal, depending on the patient’s need for anticoagulation. INR has a critical role in maintaining the warfarin response within a therapeutic range, to provide the benefits of anticoagulation, while avoiding the risks of haemorrhage (Figure 1). In liver disease, other clotting factors are decreased, so the INR does not detect or adjust to these changes.International Normalised Ratio (INR) testing is well established as an integral part of warfarin treatment. The INR is not used to monitor clients with liver disease.

A lower INR (1.3 - 1.9) may be the goal if the client is on low-dose warfarin to prevent thrombosis from a central venous catheter. Recommendations for monitoring oral anticoagulant therapy (with warfarin or acenocoumarol), are usually an INR of 2.0 - 3.0 for most clients, except those with mechanical heart valves, who require a higher INR of 2.5 - 3.5.Ĭlients usually reach an INR of 2.0 - 3.0 in 3 - 5 days after oral anticoagulation is begun.

The appropriate dose will be adjusted depending on the INR from the successive blood tests.

The INR (International Normalized Ratio) is used to monitor the dose of patients under anticoagulant therapy. INR= (Patient PT in seconds / Mean of the normal PT range for a healthy patient) ISI What is the INR test used for? INR represents the PT ratio which would have been obtained for a particular patient sample as if the WHO reference thromboplastin itself (ISI=1.0) had been used in the PT determination. The ISI, obtained from the manufacturers of the thromboplastin reagents, is used with the PT ratio to obtain the INR. This comparison of the thromboplastin from the animal source to the purer human source gives the International Sensitivity Index (ISI). In 1983, the World Health Organization (WHO) developed a plan to standardize the PT by comparing various commercial preparations of rabbit brain thromboplastin with the more sensitive human brain tissue thromboplastin. The dose of anticoagulant drugs to be prescribed may depend not only on the PT test results, but also on the lab that performs the blood test. This can be problematic when adjusting oral anticoagulant dosages based on PT test results. However, labs can use different types of thromboplastin and for that reason, the prothrombin time tests performed with different lot numbers of reagents or different methodologies may differ by 10% to 20% from one laboratory to another. To perform the prothrombin time (PT) test it is necessary to add thromboplastin to a blood sample.

One of the main role of the prothrombin time (PT) measurement is to adjust the anticoagulant medication dose in people under treatment for a cardiovascular disorder (venous thrombosis, myocardial infarction risk, pulmonary embolism, atrial fibrillation, etc.). It appears in a blood test along with prothrombin time (PT) in the coagulation screen section.Ĭoagulation cascade, also known as clotting cascade, is the process activated in the body to stop a hemorrhage (a bleeding).Īn important parameter measured to test the coagulation process is the prothrombin time (PT). INR is the acronym of International Normalized Ratio.

Warfarin inr normal range