Increased sensitivity and high specificity of indirect immunofluorescence in detecting IgG subclasses for diagnosis of bullous pemphigoid

Summary Background Indirect immunofluorescence (IIF) microscopy on monkey oesophagus is an important assay for the diagnosis of bullous pemphigoid (BP). Its relatively low sensitivity (60–80%) may be partly due to insufficient detection of minor IgG subclasses. Aim To determine the operating characteristics of an IgG subclass in IIF. Methods We designed a retrospective, dual-centre, controlled cohort study on sera from 64 BP sera that had been rated as false negatives by traditional IIF microscopy, and assessed circulating IgG1, IgG3 and IgG4 autoantibodies. Results The sensitivities of IIF in detecting IgG1, IgG3, IgG4 and all three in combination were 45.3%, 18.8%, 32.8% and 48.4%, respectively. Specificities were > 97%. Conclusion Detection of IgG subclass (especially IgG1 and IgG4) autoantibodies by IIF on monkey oesophagus can significantly improve diagnostic performance of IIF microscopy for diagnosis of BP.