The n- vs. u-serration is a learnable criterion to differentiate pemphigoid from epidermolysis bullosa acquisita in direct immunofluorescence serration pattern analysis

Summary Background Serration pattern analysis of direct immunofluorescence (DIF) allows the differentiation of epidermolysis bullosa acquisita from other subtypes of pemphigoid. In daily practice its use is limited due to lack of experience and unfamiliarity. Objectives To test the learnability of DIF serrated‐pattern recognition in groups with various a priori levels of competence. Methods An online nversusu‐test (www.nversusu.umcg.nl) was created, which contained 26 DIF images of the epidermal basement membrane zone, IgG stained and photographed with a magnification of × 40 and × 63. All images represented patients with a form of subepidermal autoimmune bullous disease. Thirteen DIF images were presented before and 13 DIF images after an instruction video about n‐ and u‐serrated patterns. There were three options to choose from: n‐serrated, u‐serrated or undetermined. The test was completed by three groups of professionals: dermatology residents in training at the University Medical Center Groningen (UMCG), international experts on bullous diseases, and dermatologists and pathologists who had participated in the Groningen blistering course during the past 10 years. Results The overall number of correct answers of serration patterns was significantly higher after instruction than before instruction (median 9·0 correct answers vs. 11·0 correct answers, P