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You can also reconfirm the diagnosis of dermatitis
hetpetiformis by taking a skin biopsy
from the skin lesions for histopathological examination and an immunofluorescence. If you are having itching alone without skin lesions, a skin biopsy from the buttock can be sent for immunofluorescence test alone, in which it should show deposits characteristic of dermatitis hetpetiformis. By doing this, you can try to avoid more invasive tests like a colonoscopy
Hope this helped you.