Prevalence and isotype distribution of antiphospholipid antibodies in Chilean patients with systemic lupus erythematosus (SLE)

Previous studies have demonstrated that ethnicity plays a role in the prevalence, isotype distribution, and clinical significance of anticardiolipin (aCL) and anti-β₂ glycoprotein I (aβ₂-GPI) antibodies in systemic lupus erythematosus (SLE) patients. Few studies have been done in Latin American populations. Serum samples from 129 Chilean SLE patients were tested for IgG, IgM and IgA aCL and aβ₂-GPI by ELISA. Clinical data were reviewed with the focus on clinical manifestations of antiphospholipid syndrome (APS). Positivity for at least one isotype of aCL was found in 30% of patients, while only 10% were positive for at least one isotype of aβ₂-GPI. IgG was the most prevalent isotype for aCL (16%), and the isotype distribution was similar (4%) for aβ₂-GPI. In general, the presence of aCL was significantly associated with the presence of aβ₂-GPI, but a number of samples were positive for only one antibody, some of them associated with clinical manifestations of APS. ACL antibodies at medium-high titers were significantly correlated with thrombosis (P/0.0007) and fetal loss (P/0.009); however, the sensitivity of aβ₂-GPI for detecting thrombosis and fetal loss was lower than aCL (19 and 17% vs 56 and 50%, respectively), and the specificity slightly higher (91 and 90% vs 84 and 82%). In Chilean SLE patients, aCL and aβ₂-GPI antibodies are important in the evaluation of patients with APS. However, the utility of aβ₂-GPI antibodies was limited by the low prevalence of these antibodies in comparison with other ethnic groups. Further studies are needed to define the basis of the observed differences among ethnic groups.