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Factor V (proaccelerin)
Last reviewed: 05.07.2025
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Reference values (norm) of factor V activity in blood plasma are 0.5-2 kU/l or 60-150%.
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. In the coagulogram, this is manifested by an increase in prothrombin time; APTT and thrombin time remain within normal limits.
Indirect anticoagulants do not have a noticeable effect on the content of factor V in the blood.
Determination of proaccelerin activity is used to identify its congenital and acquired deficiency.
Hereditary deficiency of factor V manifests itself as parahemophilia (Ovren's disease).
Factor V activity is significantly reduced in severe forms of acute viral hepatitis and in the transition of acute hepatitis to chronic. In liver cirrhosis, a distinct decrease in the content of proaccelerin in the blood plasma is observed. In uncomplicated mechanical jaundice, factor V activity is reduced, but insignificantly; with secondary involvement of the liver in the process, a distinct decrease in factor V activity occurs.
The minimum hemostatic level of factor V activity in the blood for performing operations is 25%; at a lower level, the risk of developing postoperative bleeding is extremely high. The minimum level of factor V activity in the blood to stop bleeding is 5-15%; at a lower level, stopping bleeding without administering factor V to the patient is impossible. In DIC syndrome, starting from stage II, a clear decrease in factor V activity is noted due to its consumption.
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