Wang LL, Moshiri AS, Novoa R, et al. - Researchers conducted this single-center, retrospective study to compare C3d immunohistochemistry (IHC) to direct immunofluorescence (DIF), indirect immunofluorescence (IIF), and enzyme-linked immunosorbent assay (ELISA) testing in bullous pemphigoid (BP), the most common autoimmune blistering disease, diagnosis. C3d IHC was conducted on skin biopsy specimens from 51 individuals (27 with BP and 24 with other blistering diseases) and compared with DIF and IIF, with anti-BP180 or anti-BP230 ELISA results used as the gold standard. According to results, C3d IHC, DIF and IIF were found to have similar sensitivity (74.1%, 63.1%, and 70.4%), specificity (95.8%, 100%, and 100%), positive predictive value (95.2%, 100%, and 100%), and negative predictive value (76.7%, 70.6%, and 75%) for BP. Compared with true-positive results, false-negative IIF results were linked to lower BP230. In BP diagnosis, the study compared C3d IHC with DIF and IIF, showing C3d IHC on fixed tissue offers comparable diagnostic utility to immunofluorescence and ELISA.