INR is the International Normalized Ratio that is used to monitor the effectiveness of anticoagulants. The INR ratio expresses prothrombin time, which is one of the most important parameters in the study of the coagulation system. The INR test is performed independently at home using a special apparatus, or as a component of a coagulogram (PT, PT index, INR, APTT). Exceeding the norms - too high or too low a result - requires modification of the treatment. What is the INR test?

What is the INR test?

The INR blood test is performed with a venous blood sample. The blood clotting test does not need to be performed on an empty stomach. Inform the laboratory and the doctor who interprets the INR test result about the medications you are taking. The result is obtained the day after the test.

It is possible to independently check the INR indicator at home, but you must have a special device at your disposal. Such equipment allows for the self-monitoring of INR in patients treated with anticoagulants. The measurement is very simple and is similar to self-monitoring of blood glucose with a blood glucose meter. All you need to do is prick your fingertip and collect a drop of capillary blood on the test strip.

INR (PT) - what is it?

Protombinb time helps to assess the extrinsic pathway of blood coagulation - it is mainly used to monitor anticoagulation therapy with vitamin K antagonists.

These types of tests are performed serially, but the results obtained in one patient in different laboratories may differ significantly. These discrepancies result from the individual setting of the PT standard in each laboratory.

In order to standardize the results of prothrombin time tests, the international normalized ratio (INR) was introduced.

INR test - parameters

The blood clotting system is a complex system of clotting factors, platelets, and blood vessel walls. The task of the coagulation system is to maintain the balance of blood clot formation, which takes place along the extrinsic and intrinsic pathways. In order to assess the functioning of the coagulation system, a blood test called a coagulogram is performed.

When performing the INR blood test, the following parameters are determined:

  • APTT, i.e. kaolin-kephalin time (partial thromboplastin time after activation)
  • PT, or prothrombin time
  • thrombin time
  • fibrinogen level
  • platelet count
  • concentration of D-dimers
  • levels of individual blood clotting factors

INR test - indications

The INR factor is determined primarily in patients taking anticoagulants - vitamin K antagonists.

The test is also performed in patients taking warfarin and acenocoumarol. These drugs inhibit the activity of vitamin K, and when using them, it is necessary to monitor the function of the coagulation system. Then the INR test is performed every 2-4 weeks.

INR indicator

It is routinely tested in patients prior to surgery, as well as after cardiac surgery, and in the case of stenting.

Monitoring the coagulation system by determining PT / INR is also recommended in patients at risk of developing venous thromboembolism, as well as with hepatic insufficiency.

Another indication for the blood clotting test is the occurrence of a hemorrhagic diathesis, which may be manifested by frequent bruising, prolonged menstrual bleeding, nosebleeds or increased bleeding after tooth extraction.

INR test - standard

The range of INR reference values ​​depends on the clinical condition of the patient. Under normal conditions, it is assumed thatin the INR test, the norm is 0.8-1.2 . However, the therapeutic ranges of INR in particular clinical situations are as follows:

  • prevention of deep vein thrombosis after surgery - INR in the range of 2-2.5
  • treatment of deep vein thrombosis, pulmonary embolism or transient cerebral ischemia - INR in the range of 2-3
  • heart attack, pulmonary embolism, arterial transplantation, implantation of an artificial heart valve - INR in the range of 3-4.5
  • taking anticoagulants - INR within 2-3

The INR standards apply to both adults and children. The INR standard for pregnant women is similar.

INR test - high rate

Increased INRindicates prolonged blood clotting. A high value of the prothrombin index may result from:

  • vitamin K deficiency
  • use of anticoagulants
  • liver disease
  • use of drugs that prolong blood clotting (statins, anti-acid drugs, non-steroidal anti-inflammatory drugs or some antibiotics)
  • deficiencies of fibrinogen or clotting factors (II, V, VII or X)
  • disseminated intravascular coagulation syndrome DIC

But it's worth knowing that the extended INRmay be related to a diet rich in oranges, carrots, apples, asparagus, wheat bran or milk.

INR above 5 should prompt the doctor to modify the doses of anticoagulants.

Maintaining a high INR can lead to prolonged postoperative bleeding, menstrual bleeding, vaginal bleeding, etc.

INR test - low rate

Decreased INRindicates faster blood clotting, e.g. in the course of taking:

  • estrogen
  • anticonvulsants
  • penicillins
  • dietary supplements containing vitamin K

INR below the norm may accompany the perinatal period, as well as phlebitis or thrombophilia.

Another reason is drinking St. John's wort, consuming dietary supplements containing coenzyme Q and ginseng.

Too low INR may be related to the diet, i.e. eating foods rich in vitamin K, i.e. liver, cruciferous vegetables and spinach.

When your INR is low, see your doctor.

INR test - evaluation of results

For people taking oral anticoagulants, the INR blood test is used on a regular basis. The INR result provides information on how to modify the dose of your anticoagulants:

  • INR<2 świadczy o zbyt niskiej dawce leku
  • INR in the range of 2-3 indicates the so-called therapeutic range, i.e. optimal prolongation of clotting time while minimizing the risk of bleeding
  • INR>4-5 indicates taking too high doses of medications and a high risk of bleeding dangerous to he alth and even life
  • Blood morphology - how to read the result
  • Blood tests: blood count, biochemistry, smear
  • MCH (morphology) - standard. Elevated and lowered MCH
  • MPV - standard, increased, below standard
About the authorAnna Jarosz A journalist who has been involved in popularizing he alth education for over 40 years. Winner of many competitions for journalists dealing with medicine and he alth. She received, among others The "Golden OTIS" Trust Award in the "Media and He alth" category, St. Kamil awarded on the occasion of the World Day of the Sick, twice the "Crystal Pen" in the national competition for journalists promoting he alth, and many awards and distinctions in competitions for the "Medical Journalist of the Year" organized by the Polish Association of Journalists for He alth.

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