Tests and diagnosis

By Mayo Clinic Staff

Your doctor will want to know about your past reactions to penicillin and may examine you to identify or exclude other medical problems. Unless you require penicillin — either because it's the only effective antibiotic for a life-threatening condition or because you're allergic to other antibiotics and have few treatment options — your doctor may prescribe another antibiotic.

Your doctor may recommend you be tested for penicillin allergy if:

  • You were allergic to penicillin in the past, but possibly are no longer sensitive to the drug
  • You require penicillin for treatment
  • Your doctor wants to keep you from taking a stronger antibiotic than your condition requires

Because of the risk of anaphylaxis, testing for penicillin allergy should only be done by an allergist in a hospital or doctor's office.

Skin test

This test, which can determine your sensitivity to the drug, involves the following:

  • A small amount of penicillin is injected into the skin of your forearm or back.
  • If you're allergic to the particular substance being tested, you develop a red, raised bump or reaction.

If the skin tests to penicillin are negative, your doctor may recommend penicillin or a related antibiotic. If the skin test to penicillin is positive, most likely your doctor will recommend that you continue to avoid penicillin and related antibiotics.

Blood test

Although blood tests are available for some types of allergic reaction, there aren't currently any reliable blood tests to diagnose a penicillin allergy.

Dec. 15, 2011

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