How is bullous pemphigoid diagnosed?

Bullous pemphigoid is primarily diagnosed through a skin biopsy, which reveals specific histological characteristics of the disease. This condition is an autoimmune disorder characterized by the formation of tension blisters on the skin and is generally associated with eosinophilia. A biopsy taken from the edge of a bullous lesion will typically show a subepithelial blister with a mixed inflammatory infiltrate, which prominently includes eosinophils.

Direct immunofluorescence microscopy is often performed on the skin biopsy, showing linear deposits of immunoglobulin G (IgG) and complement component C3 at the basement membrane zone, but this technique enhances the diagnosis rather than solely relying on eosinophilia.

While other diagnostic approaches—like serum ELISA for antibodies—can support the diagnosis by detecting circulating antibodies against hemidesmosomal proteins (such as BP180 and BP230), the skin biopsy with characteristic histological findings is the gold standard for confirming bullous pemphigoid. Genetic testing is not relevant in the context of diagnosing this condition, nor is patch testing, which is utilized for allergic contact dermatitis rather than autoimmune blistering diseases.