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By Mayo Clinic staffBecause it's uncommon, pemphigus can be difficult to diagnose. Blisters are common to a number of conditions, so besides taking a medical history and examining your skin and mouth, your doctor may lightly rub unblistered skin with a cotton swab or finger. With pemphigus, the top layers of your skin are likely to separate easily from the lower layers (positive for Nikolsky sign). Other tests may include:
- Skin biopsy. In this test, a piece of tissue from a blister is removed and examined under a microscope. Examination of the biopsy tissue may also involve a process called direct immunofluorescence (DIF). DIF entails staining the tissue with fluorescent dye to make the antibodies "light up" under a special microscope so that they can be identified.
- Blood tests. The purpose of these tests is to detect and identify antibodies (anti-desmogleins) in your blood.