How is bullous impetigo diagnosed?

The clinical appearance is usually suggestive but not diagnostic, and other superficial blistering or pustular disorders need to be considered, such as pemphigus, some bullous drug eruptions, and subcorneal pustular dermatosis. A Gram stain of the blister contents should demonstrate abundant Gram-positive cocci, but the definitive test is a culture that not only establishes the cause but also provides sensitivities to different antibiotics. The diagnosis can also be established by doing a biopsy, which demonstrates a subcorneal blister with neutrophils and cocci in the blister cavity.