Validating the BIOCHIP, a mosaic- based immunofluorescence test to diagnose autoimmune bullous diseases – bullous pemphigoid, pemphigus vulgaris and pemphigus foliaceous.

Background: The BIOCHIP (Dermatology Mosaic 7, EUROIMMUN, Lubeck, Germany) is a novel multiplex indirect immunofluorescence (llF) technique that has been proposed for the use of the serological diagnosis of bullous pemphigoid (BP) and pemphigus diseases. The BIOCHIP method combines the screening of autoantibodies and target antigen specific substrates in a single miniature incubation field. Objective: To validate the accuracy and measure the inter-rater reliability (lRR) of the BIOCHIP in the diagnosis of BP, pemphigus foliaceous (PF) and pemphigus vulgaris (PV). Methods: Sera from patients with BP (n=38), PF (n=8), PV (n=23), diseased control volunteers (n=64) and healthy control volunteers (n=39) were collected. The multiplex BIOCHIP was performed on all serum samples and the sensitivity and specificity was calculated. Direct immunofluorescence (DlF) for BP, PV and PF patients was performed. Additional conventional llF was performed on patients with BP and ELISA was performed on patients with pemphigus. Cohen's Kappa values were calculated to measure the level of correlation between the results of the BIOCHIP compared with the results of the gold standard methods - DIF/IIF/ELISA. 1872 digital images of each individual substrate were taken from 312 BIOCHIP slides. These were rated by ten experts from around the world with experience in the use of the BIOCHIP. Each rater rated all 1872 digital images. Raters would select options from a drop down list alongside each image. lnter-rater agreement was tested using Fleiss Kappa statistical test. Results: The BIOCHIP mosaic showed a sensitivity of 86.8% and specificity of 85.0% for BP180 or BP230 being positive in BP. A sensitivity of 75.0%and specificity of 97.7%for Dsg1 in PF and sensitivity of 60.9% and specificity of 73.6% for Dsg3 in PV. The IIR varied between fair [monkey oesophagus (MO) (k=0.257), MO pattern (k=0.357), Dsg1 (k=0.390) and BP230 (k=0.281)] and moderate [Salt-split-skin (SSS) (k=0.816), SSS location (k=0.505), Dsg3 (k=0.423) and BP180 (k=0.568)]. Conclusion: The BIOCHIP has demonstrated high validity in the diagnosis of BP and pemphigus diseases however it falls short of producing reliable results between users. lt should be used with caution as the sole method of diagnosis in BP, PV and PF