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Testing for a Drug Allergy

Most likely, your doctor can diagnose a drug allergy based on your symptoms. Sometimes, however, drug allergies are harder to pin down. In these cases, your doctor may suggest allergy testing. There are a few different types.

  • Skin tests. A doctor injects a tiny amount of the drug under your skin and watches to see if you have an allergic skin reaction. Skin tests only work for some types of drugs, like penicillin, other antibiotics, muscle relaxants, and some cancer drugs.
  • Patch testing. A doctor puts a small amount of a drug on your skin. After two to four days, the doctor will check for a reaction. This test can check for delayed allergic reactions to antibiotics, anticonvulsants, and other drugs.
  • Blood tests. Lab testing may help diagnose some allergies to antibiotics and other drugs.
  • Drug challenge tests. Your doctor gives you a small amount of the drug -- and slowly increases it -- to see how you react. You'll be under close supervision. Drug challenge tests can be dangerous, because they can trigger a serious allergic reaction. Usually, doctors only suggest them if you seem to be allergic to a drug you really need to take or if they're fairly certain that you are not allergic to the drug and want to rule it out.

Drug allergy testing can help in some cases and not in others:

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  • Test results may not give a clear answer. While skin tests are fairly accurate at showing a drug allergy, a negative test doesn’t prove you don't have the allergy.
  • There is no test for many drug allergies.
  • Many tests for drug allergies are still experimental. Experts don't know how well they really work.

WebMD Medical Reference

Reviewed by Hansa D. Bhargava, MD on October 23, 2012

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