Factors affecting cardiolipin antibody assays: modification with polyethylene glycol compound

Anti-cardiolipin antibody (aCL) measurement is only semi-reproducible, and current assays detect irrelevant as well as clinically significant antibodies. Factors found to influence results included the source of the enzyme-linked immunoabsorbent assay (ELISA) plate, and its pretreatment with solvents; the nature of the blocking solution; and the composition of the diluent used for reagents. Fetal calf serum (FCS) in the diluent appeared to reduce nonspecific (clinically irrelevant) binding and was not simply a source of beta2-glycoprotein-1 (beta2GP1). A polyethylene glycol compound was found to be an effective blocking agent, and its use enhanced the discrimination between positive and negative samples. A high level of variation may be inherent in aCL-ELISA methodology, but the use of polyethylene glycol compound appeared to be a helpful modification.