Antithrombin III is a glycoprotein, the most important natural inhibitor of blood coagulation; it inhibits thrombin and a number of activated coagulation factors (Xa, XIIa, IXa). Antithrombin III forms a fast-acting complex with heparin - heparin-ATIII. The main site of synthesis of antithrombin III is the cells of the liver parenchyma.
Thrombin time is the time required for the formation of a fibrin clot in 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 evaluates both phase III of blood coagulation - the formation of fibrin, and the state of natural and pathological anticoagulants.
Factor XIII (fibrin-stabilizing factor, fibrinase) is a β2-glycoprotein. It is present in the vascular wall, platelets, erythrocytes, kidneys, lungs, muscles, and placenta. In plasma, it is found as a proenzyme associated with fibrinogen.
An increase in fibrinogen concentration or its decrease is noted in the following conditions and diseases. Hypercoagulation at various stages of thrombosis, myocardial infarction, as well as 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 an enzymatic process under the influence of thrombin and factor XIIIa it can be converted into insoluble fibrin.
Factor V (proaccelerin) is a protein synthesized entirely 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 intrinsic (blood) prothrombinase, and activates factor X to convert prothrombin into thrombin. In cases of factor V deficiency, the extrinsic and intrinsic pathways for prothrombinase formation are disrupted to varying degrees.
Factor VII (proconvertin or convertin) is an α2-globulin and is synthesized in the liver with the participation of vitamin K. It is mainly involved in the formation of tissue prothrombinase and the conversion of prothrombin into thrombin. Its half-life is 4-6 hours (the shortest half-life among coagulation factors).
Prothrombin time characterizes phases I and II of plasma hemostasis and reflects the activity of the prothrombin complex (factors VII, V, X and prothrombin itself - factor II).
Plasma coagulation factor VIII - antihemophilic globulin A - circulates in the blood as a complex of three subunits, designated VIII-k (coagulation unit), VIII-Ag (main antigen marker) and VIII-vWF (von Willebrand factor associated with VIII-Ag). It is believed that VIII-vWF regulates the synthesis of the coagulation part of antihemophilic globulin (VIII-k) and participates in vascular-platelet hemostasis.
Factor XI - antihemophilic 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 a deficiency of factor XI, the coagulogram shows an extended blood clotting time and APTT.
