The role of serological investigations in the diagnosis of bullous pemphigoid: a retrospective study

BACKGROUND: The diagnosis of bullous pemphigoid (BP) relies on several criteria including clinical characteristics, positive findings on direct immunofluorescence microscopy (DIF) and serological tests for detect circulating IgG anti-basement membrane zone autoantibodies. METHODS: This retrospective study was conducted at the Department of Health Sciences, Section of Dermatology, University of Florence, Florence, Italy. It was designed as a multivariable and single-centered, enrolling consecutive patients with suspected BP. All eligible participants demonstrated clinical features consistent with a BP diagnosis. The participants underwent skin biopsy to obtain DIF results and a venous blood draw to secure both IIF SSS and ELISA test results. Samples were taken at the time of initial diagnosis. RESULTS: Of the 227 patients analyzed, 121 participants were diagnosed with BP, while the remaining 106 patients underwent the same diagnostic procedures but received a final negative diagnosis of BP and were included as the control group. DIF displayed the highest sensitivity and specificity (95.8% and 100%, respectively), while IIF SSS (78.3% and 98.1%) and BP180 NC16A ELISA (75.2% and 93.5%) had lower sensitivity and specificity. In terms of the combined tests' analysis results, DIF plus IIF SSS (97.0% and 99.1%) and DIF plus BP180 NC16A ELISA (99.8% and 100%) demonstrated the highest sensitivity and specificity. For combined serological tests, ELISA plus IIF SSS exhibited the highest sensitivity and specificity (88.4% and 96.7%, respectively). A cut-off of 10 IU/mL for the BP180 IgG ELISA predicted the diagnosis of BP with 100% specificity. CONCLUSIONS: Our study confirmed DIF as the preferred method for diagnosing BP. The addition of serological tests increases the diagnostic precision of DIF. Diagnosis of patients with clinical features compatible with BP may require the use of the BP180 NC16A ELISA test only in a specific setting of patients.