Prothrombin time (PT, % by Quick, INR)
Why this test?
- Recurrent miscarriages
- Vascular pathological processes
- Tendency to thrombosis
- Autoimmune diseases
- Varicose veins
- Large hematomas
- A stroke
- Fetoplacental insufficiency
- Oncological diseases
- Various disorders of the liver (including pronounced, for example, liver failure)
- Heavy menstrual bleeding
- Various infections (including sepsis), etc
In what cases is it prescribed?
- Screening testing of the coagulation system;
- suspicions/ control of blood coagulation pathology;
- control of hemostasis during drug therapy, which includes anticoagulants (both direct and indirect action);
- diagnosis of hemophilia, antiphospholipid syndrome;
- determination of fibrinogen deficiency or defect;
- monitoring the condition of a patient with DVZ-syndrome;
- selection/adjustment of the dose of acetylsalicylic acid or preparations based on it (especially in case of coronary artery disease);
- detection of secondary anticoagulants in the blood;
- examination before surgery, which is associated with a high risk of bleeding;
- pregnancy planning;
- examination during pregnancy (with a normal course, the analysis is carried out every trimester, with a complicated one - more often, as prescribed by the doctor who manages the pregnancy);
- before taking COCs with a subsequent check 1 time in 3 months;
- long-term use of glucocorticoids;
- conducting hirudotherapy, in order to prevent the occurrence of hemorrhage;
- and other indications at the doctor's discretion.
Also, pregnant women need to pass a hemostasiogram and check the state of blood coagulation before childbirth, during which a large amount of blood can be lost. If the coagulogram during pregnancy does not show the norm, this is a direct danger to the health of the expectant mother. Dangerous is both the condition when the blood does not have sufficient coagulation and the condition when increased coagulation is observed, which leads to the formation of clots and thrombus formation.
The system of hemostasis consists of many biological substances and biochemical mechanisms that ensure the preservation of the liquid state of the blood, prevent and stop bleeding. It maintains the balance between blood clotting factors.
Significant violations of the compensatory mechanisms of hemostasis are manifested by the processes of hypercoagulation (excessive thrombus formation) or hypocoagulation (bleeding), which can threaten the life and health of the patient. When tissues and vessels are damaged, plasma components (coagulation factors) participate in a cascade of biochemical reactions, the result of which is the formation of a fibrin clot.
There are internal and external pathways of blood coagulation, which differ in the mechanisms of initiation of coagulation. The internal pathway is implemented when blood components come into contact with the collagen of the subendothelium of the vessel wall. Coagulation factors XII, XI, IX and VII are necessary for this process. The extrinsic pathway is triggered by tissue thromboplastin (factor III), released from damaged tissues and the vascular wall. Both mechanisms are closely interconnected and from the moment of formation of the active factor X have common ways of implementation. The study of indicators such as PTI (prothrombin index) and INR (international normalized ratio) allows you to assess the state of the external blood coagulation pathway.
PTI is calculated as the ratio of the standard prothrombin time (the clotting time of the control plasma after the addition of tissue thromboplastin) to the plasma clotting time, expressed as a percentage.
MVN is a prothrombin test index standardized in accordance with international recommendations. It is calculated according to the formula: MNV = (prothrombin time of the patient / prothrombin time of the control) x MIC, where MIC (international sensitivity index) is the sensitivity coefficient of thromboplastin in relation to the international standard. MNV and PTI are inversely proportional indicators, that is, an increase in MNV corresponds to a decrease in PTI in the patient and vice versa. PTI reference values depend on the set and characteristics of the reagents and differ in the activity of the thromboplastin used in the test.
The results of INR determination, due to standardization, allow comparing the results of different laboratories. Tests for PTI (or an indicator close to it - prothrombin according to Kwik) and MNV in the coagulogram help to detect disorders in the external and internal pathways of blood coagulation, associated with a deficiency or defect of fibrinogen (factor I), prothrombin (factor II), factors V ( proaccelerin), VII (proconvertin), X (Stewart-Prower factor).
When the concentration of these coagulation factors in the blood decreases, the prothrombin time increases in relation to the control laboratory parameters. Plasma factors of the external coagulation pathway are synthesized in the liver. For the formation of prothrombin and some other coagulation factors, vitamin K is necessary, the lack of which leads to disturbances in the cascade of reactions and prevents the formation of a blood clot. This fact is used in the treatment of patients with an increased risk of thromboembolism and cardiovascular complications.
Due to the appointment of the indirect anticoagulant warfarin, vitamin K-dependent protein synthesis is inhibited. PTI (or prothrombin according to Kwik) and MNV in the coagulogram are used to monitor warfarin therapy in patients with factors contributing to thrombus formation (for example, deep vein thrombosis, presence of artificial valves, antiphospholipid syndrome). In a normal coagulogram in a healthy person, the MVV is within 0.8-1.2; in patients treated with indirect anticoagulants to prevent thromboembolic complications, - 2.0-3.0, in patients with prosthetic valves and antiphospholipid syndrome - 2.5-3.5. Simultaneous determination of fibrinogen in the coagulogram allows for a comprehensive assessment of the state of the plasma system of hemostasis.
Fibrinogen - blood coagulation factor I, which is produced in the liver. Thanks to the action of the coagulation cascade and active plasma enzymes, it turns into fibrin, which participates in the formation of a blood clot and thrombus. Deficiency of fibrinogen can be primary (due to genetic disorders) or secondary (due to excessive consumption in biochemical reactions), which is manifested by impaired formation of a stable thrombus and increased bleeding.
Fibrinogen is also an acute phase protein. Its concentration in the blood increases in diseases accompanied by tissue damage and inflammation. Determining the level of fibrinogen is important in the diagnosis of diseases with increased bleeding or thrombus formation, as well as for assessing the synthetic function of the liver and the risk of cardiovascular diseases with complications.