Complement Fixation Test: An Update of an Old Method for Diagnosis of Bullous Pemphigoid.

The complement fixation test (CFT) is a method traditionally used for diagnosis of gestational pemphigoid. Its performance in diagnosis of bullous pemphigoid (BP) has not been investigated in a large patient cohort. The aim of this single-centre, retrospective, serological case-control study of 300 patients with BP and 136 control patients was to analyse its operating characteristics. CFT was found to have a sensitivity of 71.7% and a specificity of 100%. Furthermore, CFT diagnosed 20 of 46 patients with BP (43.5%) who were negative for both BP180 and BP230 enzyme-linked immunoassays (ELISAs), 31 of 66 patients (47.0%) who were negative for indirect immunofluorescence of the oesophagus, 5 of 14 patients (35.7%) who were serologically negative for all investigated serological assays, and 7 of 18 patients (38.9%) in whom direct immunofluorescence was negative. Combination of CFT with all other serological assays resulted in a sensitivity of 95.3%. In conclusion, CFT is suitable for the diagnosis of BP, and can help to diagnose serologically challenging cases.