Detection of autoantibodies to the p200-epitope of SSA/Ro52 antigen. A comparison of two laboratory assays

BACKGROUND: Anti-p200 antibodies have been receiving growing interest in view of findings associating their presence to risk of fetal autoimmune congenital heart block (CHB). The study compares and evaluates the performance of two assays currently being used for their detection. METHODS: One hundred and sixteen pregnant women positive for anti-SSA/Ro52 antibodies were considered as the study population. Fifty women negative for anti-SSA/Ro52 antibodies were considered as the control population. Anti-p200 antibodies were analyzed using two home-made ELISA assays: one with biotinylated antigen and the other with free antigen. RESULTS: The specificity of the p200-free assay was significantly higher with respect to that of the p200-biotin assay (p=0.023). Both methods showed a high area under curve (AUC), thus, a good accuracy. There was a significant prevalence of anti-p200 antibodies when the p200-free assay was used to analyze the sera of the pregnant women with CHB fetuses (p=0.007). Cohen's κ and Spearman's ρ coefficients showed a good concordance (0.71) and a high correlation (0.93), respectively. CONCLUSIONS: The p200-free assay with respect to the biotin-based method was more specific in detecting p200 antibodies in women positive for anti-SSA/Ro52 antibodies. In addition, only the p200-free method significantly found p200 antibodies in patients with fetal CHB.