Image courtesy of Daniel M Peraza, MD. Diagnosis of Bullous Pemphigoid Skin biopsy and IgG titers If blisters develop, bullous pemphigoid needs to be differentiated from pemphigus vulgaris, a blistering disorder with a worse prognosis; differentiation is usually possible using clinical criteria (see Table: Distinguishing Bullous Pemphigoid From Pemphigus Vulgaris).