Measurement of factor VIII. A potential risk factor for vascular disease.

Factor VIII is a critical component of the coagulation system that is necessary for activation of factor X by factor IXa. Decreased levels of factor VIII are known to be associated with an increased risk of bleeding. It has been suggested that increased levels of factor VIII may be associated with thrombosis and atherosclerosis. Review of published studies indicates that the relationship between an increase in the level of factor VIII and atherosclerosis remains unclear at this time. While there is evidence that patients with atherosclerosis may have an increased levels of factor VIII, it is unclear if this is a primary or secondary event and whether such an increase is predictive of clinical outcome. The interpretation of epidemiologic studies is made more difficult by the current status of clinical laboratory assays for factor VIII activity. Interlaboratory proficiency surveys continue to show relatively high interlaboratory imprecision for these assays. These surveys have documented that a number of laboratories still use suboptimal methods for factor VIII assays and that use of these suboptimal methods is associated with poor performance. Improvement in factor VIII assay performance may be necessary before the role of factor VIII in atherosclerosis can be clearly defined.