Are the dermatological cut-off values of commercially available ELISAs for BP180-NC16A appropriate when applied for diagnosis of oral mucous membrane pemphigoid?. Results of a preliminary study

BACKGROUND: Enzyme-linked immunosorbent assay (ELISA) kits for BP180-NC16A use different cutoff levels established for cutaneous bullous pemphigoid (BP). However, in oral mucous membrane pemphigoid (OMMP), circulating antibodies are reported to be less readily detectable than cutaneous BP and there is little evidence that these cut-off levels are suitable for OMMP. This study was performed to explore whether the available cutoff values of anti-BP180-NC16A ELISA used for cutaneous BP are equally effective when applied to OMMP or should benefit from an optimized cut-off value. METHODS: Eighty-one patients with oral blistering diseases were divided into two groups based on the results of histological and direct immunofluorescence analyses: the OMMP group (N.=31) and the non-OMMP control group (N.=50). Antibodies against BP180-NC16A were evaluated using manufacturer's cutoff level (Euroimmun 20 U/mL). A preliminary cutoff specific for BP180 in OMMP was identified by receiver operator characteristic (ROC) curve analysis. RESULTS: A cutoff value of 20 U/mL showed low sensitivity (41.94%) but high specificity (94%). Using ROC curve analysis, a cutoff of 11 U/mL emerged as the optimal cutoff for BP180-OMMP (sensitivity: 70.97%; specificity: 88.7%). Using both cutoff values false-positives cases emerged (pemphigus vulgaris and oral lichen planus). CONCLUSIONS: The BP180-NC16A ELISA cutoff values designed for cutaneous BP may not be equally accurate when applied for the diagnosis of OMMP. The use of cut-off values specific for OMMP and a panel of several antigens specific for OMMP may improve the clinical utility of ELISAs; however, problems deriving from low specificity should be acknowledged.