A dermatologist can often diagnose granuloma annulare without any further testing. Sometimes, your dermatologist will take a small skin biopsy (taking a small piece of skin and looking at it under the microscope) to confirm the diagnosis. Rarely, people with granuloma annulare will have involvement of many parts of the skin or will have unusual forms of the condition. In these cases, your doctor might recommend some blood testing, including blood sugar (to look for diabetes), HIV testing, checking your cholesterol/blood fat levels, or checking your thyroid gland. Sometimes, they will recommend a blood cell count and routine cancer screenings (like a colonoscopy or mammogram).