Among early EM cases (≤30 days), using the C6 ELISA as the first-tier test, the prevalence of positive results by EUROLINE-RN-AT IgM blot as the second-tier test was substantially, albeit not significantly, higher than by the analogous WB IgM (93.8% vs. 62.5%), but with a slight reduction in specificity (97.6% vs. 100%). This evidence concerns the gene CD40LG and erythema multiforme.