Thromboplastin time, INR

Thromboplastin Time measures how long it takes for blood to clot. INR is short for International Normalised Ratio (P-TT-INR).

Haemostasis is a sequence of complicated events in the body, with the clotting of blood, prevention of clotting, and dissolution of the clot alternating and forming a chain reaction that aims to repair a defect in a blood vessel.

Clotting can also be harmful or unnecessary when a blood clot forms in lower limb arteries, the lungs, coronary arteries, or cerebral arteries. On the other hand, if clotting does not work in the normal way, this can lead to varying degrees of susceptibility to bleeding and bruising.

The liver produces the coagulation factors needed by the blood. Vitamin K is involved in their production. In addition, platelets (thrombocytes) and partly red blood cells (erythrocytes) play an important role in haemostasis.

The production of coagulation factors in the liver can be influenced with a drug called warfarin, which is sold under the trade name Marevan. It blocks the action of vitamin K so that coagulation factors are not produced in the liver.

When should INR be measured?

INR levels should be measured when investigating whether the patient has an increased risk of bleeding, for example due to increased bleeding and bruising, or before surgery.

Because coagulation factors are produced in the liver and liver disorders can also affect the production of coagulation factors, the INR test can be used for measuring liver function.

The dosage of Marevan is individual. The INR test can be used for examining the effectiveness of the drug in the body and adjusting the dosage, if necessary. Once control has been achieved, the INR level should be monitored in connection with injuries, changes in medication, dietary changes, smoking (starting or quitting), and sudden onset of illness, for example.

What does an INR test measure?

The INR test measures the activity of coagulation factors (II, VII, and X) that originate in the liver. These depend on the amount of vitamin K. Once anticoagulant therapy has been started and the dosage is adjusted, the change in the INR level can be seen with a delay of just a couple of days. Certain drugs (such as salicylates, clofibrate, pravastatin), alcohol, and diet affect the INR value. The higher the INR value, the slower the blood clots.