In a recent retrospective serological study in 95 sera from epidermolysis bullosa acquisita (EBA) patients Schmidt et al. conclude that Col7A-NC1/NC2 ELISA (MBL, Japan) is superior to NC1 ELISA, Western blot and indirect immunofluorescence (IIF) on salt-split skin (SSS) with the highest sensitivity of 97.9%.(1) This sensitivity is an overestimation from a biased sample, since the sera had been preselected from patients with IgG reactivity fitting EBA by at least one of the immune serological assays indirect immunofluorescence, ELISA, and Western blot. The deficiency in study design with an incorrect reference standard creates a bias in estimated test accuracy. This article is protected by copyright. All rights reserved.