Few ordinary people know the decoding of the abbreviation INR. But these three letters represent the most accurate method for evaluating the functioning of the blood coagulation system. The norms of other indicators of the coagulation system (prothrombin, fibrinogen, coagulation time and bleeding time) vary depending on gender, age, laboratory in which the study was conducted, and the reagent used. But a blood test for INR is a globally recognized indicator, unique to 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 a wound, hemorrhages in the body cavity and in internal organs. The second mechanism does not allow blood to clot too actively, thereby preventing blood clots from blocking blood vessels.
The coagulation system, or hemostasis, is divided into two types: coagulation and vascular. Vascular hemostasis is included in the work quickly, immediately after a violation of the integrity of the vascular wall. It is provided by the work of blood cells - platelets. But vascular coagulation alone is not able to completely stop the bleeding.
The next is coagulation hemostasis. 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 can 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 quantity is calculated indirectly through the following indicators of the coagulogram:
- prothrombin time;
- prothrombin index;
- prothrombin level according to Quick;
- INR.
The prothrombin index and INR are most widely used in modern medicine, since they are the most informative.
What is INR?
The acronym INR stands for International Normalized Relationship. This indicator is a more perfect derivative of prothrombin time. Prothrombin time analysis results 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. During the test, a special reagent is used 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 normal prothrombin time raised to the degree of the international sensitivity index.
Perhaps the formula sounds a little 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.
When is the test prescribed?
Determining the level of INR, like any other analysis, has strict indications for its purpose. Only a doctor can prescribe a referral. The need to take a blood test for INR occurs in the following situations:
- before the operation for the necessary preoperative preparation (the norm is from 0.85 to 1.25);
- when taking anticoagulants and antiplatelet agents (normal - from 2 to 3);
- in the treatment of pulmonary embolism (normal - from 2 to 3);
- for the prevention of thrombosis with heart defects (normal - from 2 to 3);
- patients after prosthetics of the aortic or mitral valve (normal - from 2 to 3);
- prevention of thrombosis in deep veins after surgery (normal - from 2 to 3).
Conditions in which analysis is desired
Separately, it is also worth highlighting diseases and pathological conditions in which a blood test for INR is not necessary, but in some cases the doctor may prescribe it. Among them:
- prolonged infectious diseases;
- a sharp change in lifestyle;
- change in diet;
- climate change;
- the appearance of blood in the urine;
- prolonged menstrual bleeding in women;
- frequent nosebleeds;
- causeless bruises and bruises;
- impurities of blood in the feces;
- constant appearance of blood when brushing your teeth;
- prolonged bleeding with minor injuries;
- the periodic appearance of swelling, soreness and redness of the joints, which may be associated with the accumulation of blood in them.
Principles of preparation
Preparation for a blood test for INR is not much different from that in other blood tests.
Blood sampling should be carried out in the morning, on an empty stomach. Before diagnosis, at least 8 hours refuse to take any food. You can drink only ordinary water without gas. But do not prolong starvation by more than 14 hours. This can cause a general deterioration in well-being, including 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, one hour before the examination, it is necessary to abandon this.
If the patient is taking any medications, he should consult a doctor. He will explain whether it is worthwhile to conduct a study at all or whether it is necessary to temporarily cancel the drug.
If a blood test for INR is carried out in order to diagnose clotting pathology, it must be performed before the start of drug therapy. Taking medications can distort the results of the examination.
Just before the analysis, if the nurse sees the patient’s excitement, she should tell him in detail about the examination and calm him down.
Technique and frequency of analysis
The determination of the INR level is carried out in the blood from a peripheral vein. The fence is made 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 gently draws blood into the syringe. Next, the blood is sent to the laboratory for analysis.
For patients taking anticoagulants or antiplatelet agents, an analysis is done every two to three weeks. The frequency is selected individually, depending on the severity of the disease, its duration. Patients with a well-chosen treatment regimen may 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. In both men and women, it varies from 0.85 to 1.25. On average, the INR should be 1.
Normal indicators are slightly higher for those taking antiplatelet agents and anticoagulants. Their target value of the international normalized ratio is from 2 to 3. That is, for such patients, an increase in INR is physiological and does not indicate the presence of a coagulation system pathology. But for people who are not taking drugs, any change in the INR to a greater or lesser extent indicates a disease.
Below is a table of recommended INR standards, depending on the patient's condition.
| Recommended Standards | States |
| 0.85 to 1.25 | For people not taking blood thinners |
| 1.5 to 2 | For patients with atrial fibrillation to prevent thrombosis |
| 2 to 3 | For those who are constantly taking anticoagulants |
| 3 to 4 | In the treatment of thromboembolism in the peripheral arteries |
| 3 to 4.5 | For the prevention of thrombosis after surgery using prostheses |
Reasons for an increase in INR
An increase in the international normalized ratio indicates insufficient coagulability of the blood, increasing its fluidity. This condition requires immediate action, since the development of massive bleeding is possible. Critical to raising the INR to 6.
If the patient has an elevated blood test for INR, this indicates one of the following diseases:
- congenital insufficiency of the blood coagulation system (hemophilia, idiopathic thrombocytopenic purpura);
- reduced amount of vitamin K (hemorrhagic disease of the newborn);
- severe liver disease with the development of its insufficiency;
- adverse reaction to taking certain medications: against gout, antibiotics, hormonal drugs.
Reasons for declining INR
A decrease in the results of a blood test for INR in women and men below 0.85 indicates the presence of such pathological conditions:
- change in hematocrit level;
- an increase in the concentration of antithrombin III in the blood;
- side effects when taking medications: diuretics, oral contraceptives, anticonvulsants, corticosteroids;
- blood was taken from a central catheter for analysis.
It is also possible to decrease indicators in 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.
A decrease in INR indicates hypercoagulation, that is, an increased tendency to form blood clots or emboli.
Monitoring therapy with anticoagulants using INR
Answering the question that a blood test for INR shows, it is worth saying that this is an effective method for monitoring therapy with anticoagulants and antiplatelet agents. 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 to people with a tendency to excessive blood viscosity, with an increased risk of thrombosis (myocardial infarction and stroke, congenital and acquired heart defects, 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 determining 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 a blood test for INR in men and women when taking anticoagulants is 2-3. If such a result is obtained after blood donation, the drug is taken at the same dose.
If INR has risen above this figure, it is necessary to reduce the dose of the drug. As the risk of bleeding increases.
With a decrease in INR, the dose, on the contrary, is increased. This is necessary to prevent the formation of blood clots and emboli.
Where can analysis be done?
There are several options for donating blood to determine the level of INR:
- in a private laboratory, having received a referral from a local GP or family doctor;
- directly in the therapist’s office with the necessary equipment;
- independently at home using a special apparatus.
The latter option is convenient for people who need to regularly measure INR. For example, for hemophilia patients or patients taking Warfarin and other anticoagulants. The portable device is very easy to use. Using a special device, a puncture of the skin 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 Health Organization, a blood test for INR should be performed for all patients taking drugs that affect blood coagulation. As well as those who suffer from congenital and acquired coagulation diseases.