Coagulation Factor VIII testing is used for the diagnosis of haemophilia A, the diagnosis of von Willebrand disease (together with the measurement of von Willebrand factor), the diagnosis of factor deficiencies as well as the investigation of prolonged partial thrombin activation.
Factor VIII is synthesized in the liver, circulates bound to von Willebrand factor and is part of the endogenous coagulation pathway. Its biological half-life is 9 to 18 hours. Congenital reduction of factor VIII is the cause of haemophilia A which is inherited in a residual sex-linked manner. Severe factor VIII deficiency is characterized by arthritis, extensive bleeding during injuries and sprains. Factor VIII can be reduced in von Willebrand's disease as well as in some acquired conditions. The presence of factor VIII-specific antibodies are the most common specific inhibitors of coagulation factors and can cause severe bleeding disorders (acquired haemophilia).
Whenever there is tissue damage or blood vessel injury, platelets accumulate in the area of injury. Platelets release factors that initiate the coagulation process (hemostasis). The initial type of injury dictates which pathway the process will proceed.
The endogenous pathway is involved when there is damage to the blood or blood is exposed to the collagen of the walls of the injured blood vessels. The endogenous pathway requires the sequential activation of several coagulation factors: factor XII (Hageman factor), factor XI, factor IX (Christmas factor) and factor VIII.
The extrinsic pathway begins when there is damage to the tissues or the vascular wall. In this pathway, coagulation is triggered by the release of tissue thromboplastin (factor III) from the damaged vessel or tissue cells. When this substance meets factor VII, the extrinsic pathway is stimulated.
Both pathways eventually lead to activation of coagulation factor X. This leads to the next step, in which prothrombin (factor II) is converted to thrombin (factor IIa [activated]). Thrombin then stimulates the formation of fibrin (factor Ia) by fibrinogen (factor I). This fibrin, by the addition of the fibrin stabilizing factor (XIII), forms a fixed fibrin clot at the site of injury. When the fibrin clot is no longer needed, it is dissolved by fibrinolytic agents, such as plasmin, resulting in the production of fibrin degradation products. Any of the above amounts of coagulation factors remaining after hemostasis are inactivated by fibrin inhibitors, such as antiplasmin, antithrombin III and protein C.
The action of the coagulation factors determines whether there is any congenital or acquired deficiency of each coagulation factor. These tests are useful in the diagnosis of haemophilia and coagulation disorders.
Possible Interpretations of Pathological Values
- Increase: Coronary heart disease, Cushing's syndrome, hyperthyroidism, hypoglycaemia, inflammation, advanced pregnancy, macroglobulinemia, myeloma, post-operative period, progesterone use, rebound action after abrupt catharsis, warbarin
- Decrease: Autoimmune disease, congenital deficiency, diffuse intravascular coagulation, fibrinolysis, haemophilia A, von Willebrand disease
Laboratory test results are the most important parameter for the diagnosis and monitoring of all pathological conditions. 70%-80% of diagnostic decisions are based on laboratory tests. Correct interpretation of laboratory results allows a doctor to distinguish "healthy" from "diseased".
Laboratory test results should not be interpreted from the numerical result of a single analysis. Test results should be interpreted in relation to each individual case and family history, clinical findings and the results of other laboratory tests and information. Your personal physician should explain the importance of your test results.
At Diagnostiki Athinon we answer any questions you may have about the test you perform in our laboratory and we contact your doctor to get the best possible medical care.