How is dx of bullous pemphigoid?

• Histopathology: From the edge of a blister: subepidermal blister; the inflammatory infiltrate is typically polymorphous, with an eosinophil predominance; mast cells and basophils may be prominent early in the disease course • DIF: on normal-appearing, perilesional skin • IDIF: on the patient’s serum, if the DIF result is positive • DIF: IgG and C3 deposition in a linear band at the dermal-epidermal junction, with IgG in salt-split skin found on the blister roof (epidermal side of split skin) • IDIF: circulating IgG in the patient's serum that target the skin basement membrane component