Factor VIII related antigen in the assessment of vasculitis.

Factor VIII related antigen, an endothelial cell product, was markedly raised in systemic necrotising arteritis, reflecting disease activity, but was not raised in active cutaneous vasculitis. In rheumatoid arthritis high levels were only found in systemic vasculitis or Felty's syndrome, but in other connective tissue diseases increased levels were more frequently detected and usually related to disease activity. It did not correlate with C reactive protein. It was also raised in non-inflammatory peripheral vascular disease and after surgery and was not specific for vasculitic endothelial damage. Factor VIII related antigen may be useful in identifying and monitoring systemic necrotising and large vessel arteritis.