Factor VIII Activity

Factor VIII plays a very important role in coagulation. Most of it is synthesised by the liver. It has a short lifespan (half-life of around 8 to 12 hours). In the bloodstream, FVIII is protected from too rapid degradation by the Willebrand factor.

In the coagulation cascade, FVIII combines with FIX to activate factor X. These three factors combine to form the tenase complex. The tenase complex is the main route by which thrombin and then fibrin are synthesised to form a solid clot.

In adulthood, the normal level of FVIII is between 50% and 150%; haemophilia is diagnosed when the FVIII level is below 40%. Factor VIII levels vary physiologically throughout life, even in moderate and minor haemophiliacs. It changes with age (high at birth, lowest level at around 9 months, then gradually increases with age). It also increases with inflammation, stress and pregnancy.

Haemophilia is a genetic disease that is present from birth and runs in the family. Haemophilia is said to be X-linked recessive. The FVIII gene is present on the X chromosome. Boys have only one X chromosome; if they are carriers of the genetic anomaly, they will be haemophiliacs. Girls have two X chromosomes, the second of which compensates for the deficiency, but only imperfectly. Among women with the genetic anomaly (or carriers), 2/3 will have normal factor levels, and 1/3 will have a deficiency, but generally less severe than in boys from the same family.

• Haemophilia, therefore, mainly affects men, but some women can also be affected.
• In  30% of cases, the disease is said to be sporadic, i.e. there is no known family history.
• There are rare cases of haemophilia developed due to the development of anti-factor 8 antibodies.

The severity of the disease is usually proportional to the severity of the deficiency. In severe forms of the disease and the absence of treatment, bleeding may occur spontaneously, even without trauma. Bleeding occurs mainly in the joints (haemarthrosis) and muscles (hematomas). Patients with haemophilia often need factor VIII replacement therapy to prevent or control bleeding episodes. Factor VIII activity testing is used to monitor the effectiveness of this therapy, ensuring that the patient maintains adequate levels of factor VIII to prevent bleeding complications.