Heterogeneity between Diagnostic Tests for IgA anti-Beta2 Glycoprotein I: Explaining the Controversy in Studies of Association with Vascular Pathology

IgA antibeta 2 Glycoprotein I (β2GPI) antibodies test can identify some patients with antiphospholipid syndrome (APS) that are negative for other isotypes. Controversy exists because some studies have reported a strong association of these antibodies with vascular disease, while others have not confirmed this observation. Our hypothesis is that these contradictory results may be due to differences among commercial diagnostic kits. To answer this question, we have compared the results obtained with several of the most commonly used commercial IgA anti β2GPI antibodies (aβ2GPI) diagnostic assays on specimens from individuals suspected of having APS. Sera from 69 patients (37 positive and 32 negative for IgA aβ2GPI) were analyzed with seven different commercial ELISA kits for IgA aβ2GPI, following instructions and cutoffs provided by the manufacturer. Our results showed important differences in the sensitivity and specificity of the different assays. Two of the seven kits tested had a sensitivity level below...