Introduction: Diagnosis of antiphospholipid syndrome (APS) still remains a laboratory challenge due to the great diversity of antiphospholipid antibodies (aPL) and their significance regarding APS-diagnostic criteria.
Methods: A multi-line dot assay (MLDA) employing phosphatidylserine (PS), phosphatidylinositol (PI), cardiolipin (CL), and beta2-glycoprotein I (β2 GPI) was used to detect aPL, immunoglobulin G (IgG) and immunoglobulin M (IgM) in 85 APS patients, 65 disease controls, and 79 blood donors. For comparison, anti-CL and anti-β2 GPI IgG and IgM were detected by enzyme-linked immunosorbent assay (ELISA).
Results: The level of agreement of both methods was good for anti-CL IgG, moderate for anti-CL IgM, very good for anti-β2 GPI IgG, and moderate for anti-β2 GPI IgM (kappa = 0.641, 0.507, 0.803 and 0.506, respectively). The frequency of observed discrepancies for anti-CL IgG (1.75%), anti-CL IgM (3.93%), anti-β2 GPI IgG (1.75%), and anti-β2 GPI IgM (0.87%) was low (McNemar test, P < 0.05, not-significant, respectively). Sensitivity, specificity, positive (+LR) and negative (-LR) likelihood ratios for at least one positive aPL antibody assessed by ELISA were 58.8%, 95.8%, 14.1, and 0.4, respectively, and for at least three positive aPl IgM and/or one positive aPL IgG by MLDA were 67.1%, 96.5%, 19.3, and 0.3, respectively. The frequency of IgM to PI, PS and CL, and combination of three or more aPL IgM detected by MLDA was significantly higher in APS patients with cerebral transient ischemia (P < 0.05, respectively).
Conclusions: The novel MLDA is a readily available, single-step, sensitive diagnostic tool for the multiplex detection of aPL antibodies in APS and a potential alternative for single aPL antibody testing by ELISA.