Abstract
The frequent occurrence of false positive results in the anticardiolipin (aCL) enzyme linked immunosorbent assay (ELISA) hampers its application in identifying the antiphospholipid syndrome (APS), a condition characterized by a myriad of clinical presentations. This study highlights some of the pitfalls in the use of assays for antiphospholipid (aPL) antibody in clinical practice. The aCL ELISA, commercially prepared anti-β2-gylcoprotein 1 β2-GP1) and antiphospholipid (APhL®) assays were evaluated in the diagnosis of antiphospholipid syndrome (APS) in 94 pregnant women who had spontaneous abortion and a group of 177 healthy blood donors. Serological tests were used to rule out syphilis as the cause of false positive results in the aCL ELISA. The prevalences of positive aCL ELISA results (29/94, 31% v 26/177, 14%; p = 0.001) and aCL antibodies of the IgM isotype (19/94, 20% v 6/177, 3%; $p = 0.001$) were significantly higher in aborters compared to healthy subjects. The majority of the sera which were positive in the aCL ELISA were shown to be false positives as 93% (27/29) of aCL positive aborters and 67% (8/24) of aCL positive healthy subjects were negative in the anti-β2-GP1 assay. Similarly, the sensitivity of the APhL® ELISA was low and only 1% (1/94) of the sera of aborters and 6% (11/177) of healthy subjects were positive in this assay.
The frequent occurrence of anticardiolipin antibodies of the authentic non-autoimmune variety and the low sensitivity of the other more specific aPL assays make the positive aCL ELISA difficult to interpret. We recommend that the diagnosis APS be made with strict adherence to the preliminary criteria for classification of APS.