We used a radioimmunoassay for fibrinopeptide A (FPA) to detect activation of blood clotting in patients with systemic lupus erythematosus (SLE). FPA levels were elevated in all patients with any degree of clinically detectable inflammation but were normal (< 1.5 ng/ml) or near normal in most patients in remission. The increase in concentration of plasma FPA varied directly with the number of organ systems that showed evidence of inflammation. In individual patients, changes in FPA preceded or closely paralleled changes in disease activity. We observed marked increases in FPA concentration prior to clinical exacerbations and marked decreases prior to drug-induced remissions. The activity of the clotting system as reflected by plasma FPA values appears to parallel the extent of inflammation and to provide a sensitive index of disease activity in patients with SLE.
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