The INR value is a value from laboratory medicine. It is used to assess a specific section of blood coagulation, namely extrinsic blood coagulation. It describes how fast the blood coagulates.

Figuratively speaking, it measures the extent to which and how fast the body is able to close the source of bleeding after an injury and thus stop the bleeding. In a healthy person, the INR value is around 1.0. If blood clotting takes longer than normal, the INR value rises and the risk of bleeding increases accordingly.

The INR value has replaced the previously known Quick value. The reason for this is that the quick-value was not recorded uniformly, i.e. there were fluctuations in the value depending on the laboratory where the test was performed. The INR, however, is a uniformly recorded value.

The uniformity can already be found in the name. INR means “internationally normalized ratio”. The quick value and the INR value are inversely proportional to each other.

A high Quick value therefore means a low INR value. During therapy with an oral anticoagulant, i.e. a blood thinner from the group of vitamin K antagonists, the INR is influenced. This group includes, for example, the drug Phenprocoumon, which is known as Falithrom or Marcumar®. It is used, for example, in patients with atrial fibrillation, thrombosis or pulmonary embolism, as well as artificial heart valves, to dilute the blood sufficiently to prevent the formation of a blood clot.

What is the INR used for?

The INR value is required in everyday clinical practice to monitor the blood of patients taking the blood thinner Phenprocoumon (better known as Falithrom or Marcumar®). Most patients suffer from atrial fibrillation or have an artificial heart valve. The drug is used to thin the blood and prevent the formation of blood clots.

These can lead to a stroke in the case of atrial fibrillation, for example. A common side effect of the blood-thinning drug is, however, the tendency to bleed. The patient must therefore be adjusted in such a way that no bleeding occurs despite blood thinning.

For this purpose, a value is needed that tells the treating physician how the patient is currently adjusted to the medication. It is similar to determining the blood level of a drug to find out how much of it is currently present in the body. This value is the INR value.

The normal value for healthy people is around 1.0. After adjusting to the blood thinner, the value should increase. How much the value increases depends on the disease that is treated with the medication. If the value is too low, there is a risk of a blood clot forming. If the value is too high, there is a risk of possibly serious bleeding.