What is the INR measurement in Warfarin treatment?

October 12, 2020

The World Health Organization (WHO) states that cardiovascular diseases (CVDs) are the leading cause of deaths globally. According to WHO, 31% deaths worldwide occur because of diseases related to the heart, of which 85% are caused due to heart attacks and strokes.

The severity of CVDs depends on various factors like age, weight, diet schedule, lifestyle, etc. These factors if neglected, can result in the abnormal functioning of blood cells. This dysfunction will in-turn affect the flow of the blood in arteries and veins. The substances that are responsible for preventing the formation of a clot in the blood vessels are directly affected. It thus manifests as accumulation of various compounds to form a clot that we call as a thrombi. If this clot does not stay fixed in the blood vessels, it can travel and lodge another part of the body. This is called an emboli. Be it a thrombi or an emboli, these hard-masses will impede the blood flow and hinder multiple organ systems.

A patient who is at a high-risk for developing such clots is put on an anticoagulation therapy. This therapy, which is in fact a treatment modality includes the uptake of substances known as anticoagulants. Coagulation means clotting of the blood. Anticoagulants are those that prevent the blood from clotting within the blood vessels. The most common anticoagulant used is Warfarin (a.k.a Coumadin).

Warfarin acts by blocking enzymes that facilitate the actions of blood clotting elements in the body. Hence, this avoids the blood from clotting. However, the action of the warfarin within the body may also vary, since it actively interacts with medications and certain food sources that we regularly take. This can lead to the blood thinning to an extent that it leads to profuse bleeding and eventual damage of various tissues. Hence, when a patient is on warfarin, it is important to balance it with supplements that also maintain a certain level of clotting mechanism in the body. In order to standardize a perfect range for warfarin dosage, the International Normalized Ratio (INR) was introduced.

When a patient sends a blood test report, a commonly investigated test is prothrombin time. Prothrombin is a key protein in the body which is produced in the liver and is responsible for the clotting of blood. A prothrombin time helps in knowing the time that the blood takes to develop into a clot. However, this factor can vary in patients who are on anticoagulant therapy. Hence, in order to standardize the results of prothrombin time, the INR was devised.

The INR is calculated by a formula that sees the prothrombin time of the patient be divided with normal prothrombin time. This is later squared to the power of International Sensitivity Index (ISI) which varies between 1.0 to 2.0. The INR value ranges from 0.0 to 5.0. The ideal range is between 2.0 to 3.0, which means that the coagulation system is appropriate.

If the number is below 2.0, it means that the blood is thicker in consistency and clot formation can take place. The dosage of warfarin in this case needs to be increased. Patient should not eat a diet that are sources of Vitamin K since they contribute to coagulation.

If the number is above 3.0 it means the blood is thin enough to manifest a risk of bleeding. In this case, the patient's warfarin dose should be decreased or stopped. If the patient is consuming alcohol regularly, he or she needs should be advised to abstain from it. Moreover, such patients are often advised to take supplements of Vitamin K, that aids in the coagulation process. It is important to tell the patient to avoid taking common medications like aspirin that will further increase the chances of bleeding in this scenario.

It is important to note that if a patient is scheduled for any medical or dental surgery, he or she should inform the healthcare provider regarding the warfarin/anticoagulation therapy. This is crucial as surgical procedures might become complicated if the INR is in an abnormal range. In dentistry, procedures like extraction of tooth or any procedure that involves incising the gums should be carefully carried out in patients on anticoagulation therapy. A fresh test of INR may be needed and the patient will be scheduled accordingly.

INR values may also vary if a patient already has an underlying disease or condition. For example, in the disorders of the thyroid gland, INR values increase in hyperthyroidism and decrease in hypothyroidism. Moreover, diseases of the liver can decrease the INR value.

The INR helps in monitoring the warfarin therapy. It should be ensured that the patients get their INR testing done regularly when on warfarin treatment in order to avoid any unnecessary complications.

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