Serin-Prothrombin-Check is a solid phase enzyme immunoassay with highly purified phosphatidyl-serine plus native human prothrombin for the combined quantitative and qualitative detection of IgG and IgM antibodies against phosphatidyl-serine and prothrombin in human serum. The assay is an aid in the diagnosis and risk estimation of thrombosis in patients with systemic lupus erythematosus and anti-phospholipid syndrome (APS).