Antithrombin III is a glycoprotein, the most important natural inhibitor of blood coagulation; inhibits thrombin and a number of activated clotting factors (Xa, XIIa, IXa). Antithrombin III forms a high-speed complex - heparin-ATIII - with heparin. The main site for the synthesis of antithrombin III is the liver parenchyma cells.
Thrombin time is the time required to form a fibrin clot in the plasma when thrombin is added to it. It depends only on the concentration of fibrinogen and the activity of thrombin inhibitors (ATIII, heparin, paraproteins) and assesses both the phase of blood coagulation - the formation of fibrin, and the state of natural and pathological anticoagulants.
Factor XIII (fibrin-stabilizing factor, fibrinase) refers to β2-glycoproteins. It is present in the vascular wall, platelets, erythrocytes, kidneys, lungs, muscles, placenta. In plasma it is in the form of a proenzyme, connected with fibrinogen.
An increase in the concentration of fibrinogen or its reduction is noted in the following conditions and diseases. Hypercoagulation at various stages of thrombosis, myocardial infarction, and also in the last months of pregnancy, after childbirth, after surgical operations.
Fibrinogen (factor I) is a protein synthesized mainly in the liver. In the blood, it is in a dissolved state, but as a result of the enzymatic process, under the influence of thrombin and factor XIIIa it can turn into insoluble fibrin.
Factor V (proaccelerin) is a protein fully synthesized in the liver. Unlike other factors of the prothrombin complex (II, VII and X), its activity does not depend on vitamin K. It is necessary for the formation of internal (blood) prothrombinase, activates factor X for the conversion of prothrombin to thrombin. In cases of factor V deficiency, the external and internal pathways for the formation of prothrombinase are disturbed to varying degrees.
Factor VII (proconvertin, or convertinum) refers to α2-globulins and is synthesized in the liver with the participation of vitamin K. It is mainly involved in the formation of tissue prothrombinase and the transformation of prothrombin into thrombin. Its half-life is 4-6 hours (the shortest half-life among the coagulation factors).
Prothrombin time characterizes the I and II phases of plasma hemostasis and reflects the activity of the prothrombin complex (factors VII, V, X and prothrombin itself - Factor II).
The plasma clotting factor VIII - anti-hemophilic globulin A - circulates in the blood in the form of a complex of three subunits, designated VIII-k (coagulating unit), VIII-Ar (the main antigen marker) and VIII-PV (von Willebrand factor bound to VIII-Ar ). It is believed that VIII-FV regulates the synthesis of the coagulation part of anti-hemophilic globulin (VIII-k) and participates in vascular-platelet hemostasis.
Factor XI - anti-hemophilic factor C - glycoprotein. The active form of this factor (XIa) is formed with the participation of factors XIIa, Fletcher and Fitzgerald. Form XIa activates factor IX. With the deficiency of factor XI in the coagulogram, the coagulation time of the blood and APTT is prolonged.
