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Factor VIII (antihemophilic globulin A)
Last reviewed: 04.07.2025
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Reference values (norm) of factor VIII activity in blood plasma are 60-145%.
Plasma coagulation factor VIII - antihemophilic globulin A - circulates in the blood as a complex of three subunits designated VIII-k (coagulation unit), VIII-Ag (the 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 VIII is synthesized in the liver, spleen, endothelial cells, leukocytes, kidneys and participates in phase I of plasma hemostasis.
Determination of factor VIII plays a key role in the diagnosis of hemophilia A. The development of hemophilia A is due to a congenital deficiency of factor VIII. In this case, there is no factor VIII in the blood of patients (hemophilia A - ) or it is in a functionally defective form that cannot participate in blood clotting (hemophilia A + ). Hemophilia A - is detected in 90-92% of patients, hemophilia A + - in 8-10%. In hemophilia, the content of VIII-k in the blood plasma is sharply reduced, and the concentration of VIII-vWF in it is within the normal range. Therefore, the duration of bleeding in hemophilia A is within normal limits, and in von Willebrand disease it is increased.
Hemophilia A is a hereditary disease, but 20-30% of patients do not have a positive family history. Therefore, determining the activity of factor VIII has great diagnostic value. Depending on the level of factor VIII activity, the following clinical forms of hemophilia A are distinguished: extremely severe - factor VIII activity up to 1%; severe - 1-2%; moderate - 2-5%; mild (subhemophilia) - 6-24%.
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