Frequency of antiphospholipid antibodies in patients with infectious diseases using three different ELISA methods

Abstract

OBJECTIVE: The standard enzyme-linked immunosorbent assay (ELISA) for anticardiolipin (aCL) antibodies is the most important test for the diagnosis of antiphospholipid syndrome (APS). However, the test is also positive in some infectious diseases and other non-related syndromes. It has been suggested that the detection of antibodies to a mixture of phospholipids or to b2-glycoprotein I (b2-GP I) has higher specificity for APS than the standard aCL ELISA. The aim of the present work is to compare the diagnostic specificity of three different antiphospholipid (aPL) assays in patients with infectious diseases. METHODS: Antiphospholipid antibodies were searched by three ELISA techniques, namely standard aCL, APhL® ELISA kit and anti-b2-GP I, in sera of patients with infectious diseases, including syphilis (69), leptospirosis (33) and visceral leishmaniasis (30). RESULTS: The frequency of positivity of IgG aPL in patients with syphilis, leptospirosis and Kala-azar was 13/69 (19%), 9/33 (27%) and 2/30 (6%), respectively, using standard ELISA, versus only 1/69 (1.4%), 0/33 (0%) and 0/30 (0%) positivity by the APhL® ELISA kit. The positivity of the isotype IgM aPL was 10/69 (14%), 4/33 (12%) and 1/30 (3%), respectively, by the standard ELISA, and 1/69 (1.4%), 0/33 (0%) and 0/30 (0%) by the APhL® ELISA kit. The presence of significant levels of IgG anti-b2GPI was observed in 14/69 cases of syphilis (20%), 6/33 cases of leptospirosis (18%) and 16/30 cases of Kala-azar (53%). The APhL® ELISA kit had superior performance showing the highest specificity: 97% (95% CI: 92%-99%) for IgG compared to 81% (95% CI: 74%-87%) for standard ELISA and 72% (95% CI: 64%-79%) for anti-b2 GPI assay. CONCLUSIONS: The APhL® ELISA kit proved to be significantly more specific than the aCL standard ELISA and the anti-b2GPI ELISA, and it should be used to help in the diagnosis and confirmation of APS.