Both chickenpox (varicella) and shingles (zoster) can usually be diagnosed by symptoms alone. If a diagnosis is still unclear after a physical examination, laboratory diagnostic tests may be required. These tests use samples of fluid taken from the blister. They are generally used to distinguish between varicella-zoster and herpes simplex viruses.
Ruling out Other Disorders
Ruling out Disorders that Resemble Chickenpox. Chickenpox, particularly in early stages, may be confused with herpes simplex, impetigo, insect bites, or scabies.
Ruling out Disorders that Resemble Shingles. The early prodrome stage of shingles can cause severe pain on one side of the lower back, chest, or abdomen before the rash appears. It therefore may be mistaken for other disorders, such as gallstones, that cause acute pain in internal organs.
In the active rash stage, shingles may be confused with herpes simplex, particularly in young adults, if the blisters occur on the buttocks or around the mouth. Herpes simplex, however, does not usually generate chronic pain.
A diagnosis may be difficult if herpes zoster takes a non-typical course in the face, such as with Bell's palsy or Ramsay Hunt syndrome, or if it affects the eye or causes fever and delirium.