One of the most commonly used ways to diagnose shingles is by looking for its fairly unique symptoms. Shingles usually starts by causing a very severe burning or tingling pain that is limited to one side of the body or face. After the pain begins, a rash develops on the affected parts of the body. This rash then progresses into small blisters. The blisters then break and form small open sores (also known as skin ulcers) that crust over. Typically the crusts begin to fall off after two to three weeks. In general, shingles doesn't cause any scarring. These symptoms, especially in patients who have already had chickenpox, are usually enough for a diagnosis.
Another way of testing to detect shingles in a patient can be done with a blood test. The first step is a procedure called a complete blood count, which can identify increased levels of white blood cells in the blood. Because white blood cells are needed to fight off the herpes zoster re-infection, this suggests the pain and rash are caused by some infectious agent. If elevated white blood cells are observed, your doctor may test your blood for antibodies to the herpes zoster virus. Antibodies are proteins that your body makes due to infections and can be detected by laboratory tests. Elevated levels of antibodies to the herpes zoster virus suggests that the symptoms are caused by shingles but it does not definitively diagnose the cause.
If there is any uncertainty as to whether the patient's symptoms are caused by shingles and the blood tests indicate that shingles might be present, doctors may take a sample of the tissue from the blisters or ulcers. The doctor will scrape the area of the skin lesion and have someone look at the cells under a microscope. Skin cells that have become infected with herpes tend to have an altered appearance and may be larger and misshapen. These characteristic changes can tip off a lab technician that the skin problems are caused by shingles.