Few ordinary people know the decoding of the abbreviation INR. But these three letters represent the most accurate method for assessing the work of the blood coagulation system. The norms of other indicators of the coagulation system (prothrombin, fibrinogen, clotting time and bleeding time) vary depending on gender, age, laboratory in which the study was conducted, and the reagent used. But the INR blood test is a worldwide recognized indicator, the only one for all laboratories.
Blood coagulation system
To understand the indicators of a blood test for INR, you need to know how the blood coagulation and anticoagulation systems work. The first mechanism prevents the development of excessive blood loss from the wound, hemorrhages in the body cavity and internal organs. The second mechanism prevents blood from clotting too actively, thereby preventing blockage of blood vessels by blood clots.
The coagulation system, or hemostasis, is divided into two types:coagulation and vascular. Vascular hemostasis is activated quickly, immediately after the violation of the integrity of the vascular wall. It is provided by the work of blood cells - platelets. But vascular clotting alone will not permanently stop the bleeding.
The coagulation hemostasis is connected next. This mechanism exists due to the functioning of special proteins - coagulation factors. They are synthesized by liver cells. Therefore, with its diseases (hepatitis, cirrhosis), excessive bleeding occurs. Only the work of these proteins is able to ensure the final stop of bleeding.
Methods for diagnosing the state of the blood coagulation system
The main way to check the condition of the bloodstream is a coagulogram. One of its most significant indicators is the level of prothrombin, or coagulation factor II. It is produced in the liver under the influence of vitamin K.
The level of prothrombin in the blood cannot be calculated directly. Its amount is calculated indirectly through the following indicators of the coagulogram:
- prothrombin time;
- prothrombin index;
- quick prothrombin level;
- MNO.
The prothrombin index and INR are the most widely used in modern medicine, as they are the most informative.
What is INR?
The abbreviation INR stands for "International Normalized Ratio". This indicator is a more perfect derivative of prothrombin time. resultsprothrombin time assays differ depending on the reagent used. Therefore, it was decided to standardize this indicator. For this purpose, they came up with a blood test for INR. The test uses a special reagent that takes into account the international sensitivity index.
What does an INR blood test mean? This indicator is calculated as follows: the ratio of the patient's prothrombin time to the normal prothrombin time raised to the power of the international sensitivity index.
Maybe the formula sounds a bit cumbersome and scary. But thanks to its development, the patient can do this test in different laboratories, cities and even countries, which will not affect the final result in any way.
When is the test ordered?
Determination of the INR level, like any other analysis, has strict indications for its purpose. Only a doctor can write a referral. The need to take a blood test for INR occurs in the following situations:
- before surgery to carry out the necessary preoperative preparation (the norm is from 0.85 to 1.25);
- when taking anticoagulants and antiplatelet agents (the norm is from 2 to 3);
- in the treatment of pulmonary embolism (normal - from 2 to 3);
- for the prevention of thrombosis in heart defects (the norm is from 2 to 3);
- patients after aortic or mitral valve replacement (normal - from 2 to 3);
- prevention of thrombosis in deep veins after surgery (normal - from 2 to 3).
Conditions in which it is desirable to take the test
Separately, it is also worth highlighting diseases and pathological conditions in which a blood test for INR is optional, but in some cases a doctor may prescribe it. Among them:
- protracted infectious diseases;
- dramatic lifestyle change;
- changing diet;
- climate change;
- blood in urine;
- prolonged menstrual bleeding in women;
- frequent nosebleeds;
- uncaused bruises and bruises;
- blood in feces;
- constant appearance of blood when brushing teeth;
- prolonged bleeding from minor injuries;
- periodic appearance of swelling, pain and redness of the joints, which may be due to the accumulation of blood in them.
Principles of preparation
Preparation for an INR blood test is not much different from that of other blood tests.
Blood sampling should be done in the morning, on an empty stomach. Before the diagnosis, they refuse to take any food for at least 8 hours. You can drink only plain water without gas. But you should not prolong fasting for more than 14 hours. This can cause a deterioration in general well-being, up to fainting.
Eliminate alcohol at least one day before the examination. It is also advisable to limit the intake of fatty and heavy foods at this time. If the patient smokes, stop smoking one hour before the examination.
If the patient is taking any medication, they shouldconsult a doctor. He will explain whether it is worth conducting a study at all or whether it is necessary to temporarily stop the drug.
If an INR blood test is performed to diagnose a clotting pathology, it should be done before starting drug therapy. Taking medications can distort the results of the examination.
Immediately before the analysis, if the nurse sees the patient's excitement, she should tell him in detail about the examination and reassure him.
Technique and frequency of analysis
Determination of the level of INR is carried out in the blood from a peripheral vein. The sampling is done with a disposable, sterile syringe. The skin before the injection is treated with an antiseptic solution. A tourniquet is applied to the forearm, and the nurse carefully draws blood into a syringe. The blood is then sent to a laboratory for analysis.
Patients taking anticoagulants or antiplatelet agents are tested every two to three weeks. The frequency is selected individually, depending on the severity of the course of the disease, its duration. Patients with a well-chosen treatment regimen can be tested once a month.
Normal analysis values
The norm of a blood test for INR in adults does not depend on age or gender. For both men and women, it varies from 0.85 to 1.25. On average, the INR should be 1.
Somewhat higher than normal in those who take antiplatelet agents and anticoagulants. Their target value of the international normalized ratio is from 2 to 3. That is, for such patientsan increase in INR is physiological and does not indicate the presence of a pathology of the coagulation system. But for people not taking drugs, any change in INR up or down indicates some kind of disease.
Below is a table of recommended INR norms depending on the patient's condition.
| Recommended rates | States |
| From 0.85 to 1.25 | For people not taking blood thinners |
| From 1, 5 to 2 | For patients with atrial fibrillation to prevent thrombosis |
| From 2 to 3 | For those who constantly take anticoagulants |
| 3 to 4 | In the treatment of thromboembolism in peripheral arteries |
| 3 to 4, 5 | For the prevention of thrombosis after surgical interventions with the use of prostheses |
Reasons for increasing INR
An increase in the international normalized ratio indicates insufficient blood clotting, an increase in its fluidity. This condition requires immediate action, as massive bleeding is possible. Critical is the rise of INR to 6.
If a patient has an elevated INR blood test, this indicates one of the following diseases:
- congenital insufficiency of the blood coagulation system (hemophilia, idiopathic thrombocytopenic purpura);
- reduced amount of vitamin K (hemorrhagic diseasenewborn);
- severe liver disease with development of liver failure;
- Adverse reaction to certain medications: against gout, antibiotics, hormonal drugs.
Reasons for lowering INR
A decrease in blood test results for INR in women and men below 0.85 indicates the presence of such pathological conditions:
- change in hematocrit;
- increase in the concentration of antithrombin III in the blood;
- side effects when taking medications: diuretics, oral contraceptives, anticonvulsants, corticosteroids;
- blood taken for analysis from a central catheter.
It is also possible to reduce the indicators in case of violation of the technique of conducting a blood test for INR. For example, if the blood plasma was at a temperature of +4 °C for a longer time than required.
Reducing the level of INR indicates hypercoagulation, that is, an increased tendency to form blood clots or emboli.
Control of anticoagulant therapy with INR
Answering the question of what the INR blood test shows, it is worth saying that this is an effective method for monitoring anticoagulant and antiplatelet therapy. These two groups of drugs thin the blood. Therefore, it is necessary to constantly monitor the state of the blood coagulation system in order to prevent the development of severe bleeding. This is especially true for treatment with such drugs:
- "Heparin";
- "Warfarin";
- "Sinkumar";
- "Finilin".
Anticoagulants are prescribed for people with a tendency to excessive blood viscosity, with an increased risk of thrombosis (myocardial infarction and stroke, congenital and acquired heart defects, a history of pulmonary embolism, varicose veins, thrombophlebitis).
Changing the dosage of anticoagulants depending on the level of INR
We have already figured out what a blood test for INR means. We found out the reasons for the increase and decrease in the indicator. It was also noted that the determination of the level of INR is the most effective way to control anticoagulant therapy. How to correct treatment after receiving the results of the analysis?
The norm of blood test for INR in men and women when taking anticoagulants is 2-3. If such a result is obtained after donating blood, the drug is taken at the same dose.
If the INR has risen above this figure, it is necessary to reduce the dose of the drug. Because the risk of bleeding increases.
When INR decreases, the dose, on the contrary, is increased. This is necessary to prevent the formation of blood clots and emboli.
Where can I do the analysis?
There are several options for donating blood to determine the level of INR:
- in a private laboratory with a referral from a GP or family doctor;
- directly in the therapist's office with the necessary equipment;
- on their own at home using a special apparatus.
The last option is convenient for people who need to measure INR regularly. For example, for patients with hemophilia or patients taking Warfarin and other anticoagulants. The portable device is very easy to use. With the help of a special device, a skin puncture is made, and blood is applied to the test strip. The strip is inserted into the device, and almost immediately the result appears on the display.
According to the recommendations of the World He alth Organization, an INR blood test should be performed in all patients taking drugs that affect blood clotting. And also for those who suffer from congenital and acquired clotting diseases.
