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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.

Normally, the result is:

Reference values:

  • 0.9–1.2
  • Therapeutic range 2–3 INR Prevention or treatment of arterial thrombosis (a blood clot in an artery)
  • Therapeutic range 2.5–3.5 INR In connection with a mechanical valve

Please contact your physician or other healthcare professional if you suspect an illness or need help interpreting the results.

Read more about defining reference values.

The higher the INR value, the slower the blood clots. This can be caused by an excessively high amount of warfarin, or when coagulation factors dependent on vitamin K (II, VII, and X) are not produced in the normal way in the liver because of liver failure or vitamin K deficiency, for example.

The lower the INR value, the faster blood clots and the bigger the risk of blocked veins.

  • Basic blood count and thrombocytes provide an overview of red and white blood cells and platelets (2474 B-PVK+T)
  • Thromboplastin time, activated, partial (2783 P-APTT)
  • Fibrin D-dimer indicates arterial thrombosis (4113 P-FiDD)
  • Fibrinogen (1399 P-Fibr)

SYNLAB test list: Thromboplastin time (4520 P -TT-INR, 1731 P-TT) https://www.yml.fi/tuotekuvaus_show.php?tuotenro=359

Terveyskirjasto health library: INR https://www.terveyskirjasto.fi/terveyskirjasto/tk.koti?p_artikkeli=ltt01358&p_hakusana=inr

Terveyskirjasto health library: Tromboplastiiniaika (P-INR) https://beta.terveyskirjasto.fi/snk03040?q=inr

Terveyskirjasto health library: Syvä laskimotukos ja keuhkoembolia eli veritulppahttps://www.terveyskirjasto.fi/terveyskirjasto/tk.koti?p_artikkeli=khp00046&p_hakusana=inr

Terveyskirjasto health library: Verenohennuslääkkeet (antikoagulaatiohoito) https://www.terveyskirjasto.fi/terveyskirjasto/tk.koti?p_artikkeli=dlk00007


Fasting is not required

This examination does not require fasting