To diagnose shingles, a physician will take the patient’s complete medical history and perform a physical examination. Observance of blisters or rash from shingles is often all that is necessary to permit a diagnosis. However, a doctor may choose to perform tests for confirmation, including:

• Tzanck smear. Opening a blister to collect fluid and skin cells for analysis under a microscope. A Tzanck smear may reveal viral changes in cells, though it cannot distinguish varicella-zoster virus (VZV) from herpes simplex virus (HSV) and may not be appropriate for all patients.
  
  
• Direct fluorescent antibody (DFA) test. A test that detects substances in the body that produce an immune response. DFA testing differentiates between VZV and HSV and may be useful in diagnosing shingles, though it is seldom necessary.
  
  
• Skin biopsy. Collection of a sample of skin rash for microscopic analysis. Cultures of biopsied tissue may also be performed if there are no unbroken blisters available. DNA (deoxyribonucleic acid) indicating VZV may be detected with a skin biopsy.

When patients seek medical attention for their symptoms before the rash appears, diagnosis may be difficult. In fact, the severe pain that often precedes the rash is often misdiagnosed as a result of kidney stones, gallstones, appendicitis, heart attacks and other conditions.