Coagulation tests – method of complex investigation of the hemostasis system. Coagulation tests may include a set of various indicators, the main of which are prothrombin time, thrombin time, clotting time, fibrinogen, antithrombin III, lupus anticoagulant, APTT, D-dimer, prothrombin index, etc.
Coagulation tests in cardiology has diagnostic value in myocardial infarction, assessment of the risk of bleeding, thrombosis; planning of cardio- and angiosurgical interventions, therapy with anticoagulants of indirect and direct action. Coagulation tests may include a set of various indicators, the main of which are prothrombin time, thrombin time, clotting time, fibrinogen, antithrombin III, lupus anticoagulant, APTT, D-dimer, prothrombin index, etc. Venous blood is taken for coagulation tests examination on an empty stomach.
Any changes in hemostasis are fraught with dangerous consequences: an increase in the rate of clotting is accompanied by thrombosis, and, as a result, an increased risk of strokes and heart attacks; lengthening the time of formation of a blood clot indicates the likelihood of bleeding. Until a certain time, violations of the hemostasis system may not clinically reveal themselves, therefore, on the recommendation of a doctor, a coagulation tests should be periodically monitored.
Indications
Coagulation tests is prescribed to assess the risk of bleeding and thrombosis before childbirth or surgical interventions. Coagulation analysis is widely used by cardiology and vascular surgery. Coagulation tests is necessary for various vascular pathologies (varicose veins, thrombophlebitis), liver, heart (coronary artery disease, infarction), blood clotting, autoimmune disorders. Evaluation of coagulation tests parameters is extremely important in the treatment of anticoagulants (fraxiparin, heparin, syncumar, phenylin, warfarin, etc.), the selection of dosage of acetylsalicylic acid preparations (cardiomagnil, thrombo ASS).
In the management of pregnancy, the study of coagulation tests is mandatory once a trimester, more often – with gestosis or fetoplacental insufficiency. This analysis is an integral part of the monitoring of the hemostasis system and the assessment of thrombosis factors when using oral contraception (it is examined once every three months). Coagulation tests is monitored during hirudotherapy to evaluate the treatment and prevention of hemorrhage.
Preparation for analysis
The material for the analysis of coagulation tests is peripheral venous blood. Before the planned study, the patient is recommended to abstain from eating and drinking (juice, alcohol, coffee) for 8-12 hours. It is allowed to drink ordinary water. If the examinee takes medications that affect blood clotting, this is marked in the direction of the analysis. The interpretation of individual and aggregate parameters is carried out by a doctor.
Key indicators
The study can be carried out by various methods, therefore, the set of parameters is variable. The basic parameters are fibrinogen, ACTV, lupus anticoagulant, thrombin time, prothrombin time, antithrombin III, D-dimer, clotting time (bleeding), prothrombin.
Fibrinogen is a protein, a precursor of fibrin, which is the basis of a blood clot. Fibrinogen (normally 2.0-4.0 g / l) increases with inflammation and necrosis of tissues, which indicates the risk of cardiovascular catastrophes due to increased clotting. A decrease in fibrinogen is noted with a tendency to congenital hemorrhages, with liver dysfunction, DIC syndrome, etc.
The APTT indicator (activated partial thromboplastin time, norm 24-35 sec.) is a screening test of clotting, important for patients receiving heparin in the diagnosis of DIC syndrome. In this test, the rate of blood clot formation is determined when certain reagents are added. A decrease in APTT is a factor of high clotting and a tendency to thrombosis. The lengthening of the APTT indicates a decrease in clotting and the risk of bleeding.
Lupus anticoagulant is a group of antibodies (IgG and IgM) to the outer platelet membrane. Normally, lupus anticoagulant is not determined during the study coagulation tests. Its presence may be associated with autoimmune disorders, pregnancy pathology (gestosis) and lead to thrombosis of arteries and veins. Determination of lupus anticoagulant during pregnancy is a risk factor for spontaneous abortion, placental infarction, pod death.
The parameter coagulation tests – thrombin time – indicates the rate of transition of fibrinogen to fibrin under the influence of thrombin. An increase in thrombin time (at a norm of 11-17.8 seconds) may be associated with a deficiency of fibrinogen, the presence of fibrinogen inhibitors, thrombin or heparin.
The definition of prothrombin time in coagulation tests reflects the time of transition of prothrombin to its active substance – thrombin. An increase in prothrombin time in comparison with the norm (11-16 seconds) indicates a deficiency of vitamin K, a lack of clotting factors, liver diseases.
As a natural anticoagulant, antithrombin III inhibits the clotting factor thrombin. Antithrombin III (norm 71-115%) is examined in a coagulation tests to assess the anticoagulation system, determine the tendency to thrombosis, and control treatment with heparin. Its increase is usually associated with acute hepatitis, mechanical jaundice, menstruation, inflammation; decrease – with congenital deficiency, DIC syndrome, liver failure.
D-dimer, as a product of fibrinolysis, is important in the diagnosis of thrombosis. Normally, the D-dimer in coagulation tests is less than 248 ng /ml, indicating the processes of thrombosis and destruction of fibrin.
One of the basic parameters is the clotting time is determined by the rate of stopping bleeding after a puncture of the skin (the norm is 2-3 min.). An increase in clotting time indicates thrombocytopenia, violations of platelet aggregation and adhesion, liver diseases, connective tissue, kidneys.
The determination of the coagulation factor – prothrombin in coagulation tests reflects the state of hemostasis. Excess of the norm of prothrombin (78-142%) threatens the development of thrombosis.
The calculated parameters include INR and PTI. The international normalized ratio (INR is normally 0.8-1.2) is the ratio of the obtained prothrombin time to its average normal value. It is studied in a coagulation tests during therapy with anticoagulants. A decrease in INR indicates an increased risk of thrombosis, an increase indicates a tendency to bleeding.
The value of the prothrombin index (PTI) is calculated by the ratio of the normal clotting time to that of this patient. PTI, expressed as a percentage (the norm is 80-120%), increases with a tendency to thrombosis, decreases with a tendency to hemorrhages.
