Diagnostic value of direct immunofluorescence of mucosal and skin biopsy specimens on formalin-fixed paraffin-embedded biopsy specimens compared to specimens placed in normal saline as the gold standard method in the diagnosis of a group of autoimmun

Background and Aim: Direct immunofluorescence (DIF) is represented as a gold standard method in diagnosis of autoimmune blistering dermatoses. Normal saline, liquid nitrogen and michel’ solution are a widely accepted media for preserving biopsy samples of skin or mucosa before DIF examination. Occasionally clinicians put the biopsy specimen taken for DIF in formalin 10%, occasionally clinicians ordered DIF retrogradely and only a paraffin-embedded biopsy specimen exposed to formalin 10% is available. To determine the diagnostic value of DIF when it was performed on biopsy samples of skin or mucosa exposed to formalin 10% in comparison to the same biopsy samples exposed to normal saline.   Methods: In 74 patients (38 immunobullous and 23 chronic dermatitis), which the latter served as the normal controls, 2 perilesional punch biopsy of skin or mucosa were done, one put in formalin 10% and fixed in paraffin and one put in normal saline, and DIF was done on both samples.    Results: DIF sensitivity and specificity was with IgG 31.5% and 100% in pemphigus and 15.36% and 93.44% in BP, with C3 39.47% and 100% in pemphigus and 7.69% and 91.80% in BP, respectively.   Conclusion: DIF on specimens exposed to formalin 10% in comparison to specimens exposed to normal saline is less sensitive but approximately as specific as it is in the diagnosis of pemphigus and BP patients and especially can be useful in pemphigus patients when only a formalin exposed samples is available.