Skin Pricks, Blood Tests Not as Reliable as Food in Testing for Allergies

December 26, 2011 — -- A simple skin-prick or blood test has confirmed many people's suspicions that they have certain food or seasonal allergies, but a study published Monday in the journal Pediatrics suggests that allergy diagnoses should not be made solely on results from such tests.

Skin or blood tests remain the only method used to diagnosis allergies for some, the researchers wrote. And in some cases, patients who never exhibited symptoms are still tested for allergies.

About 3 percent of adults and 6 percent of young children have at least one food allergy, according to the National Institutes of Health.

Eating small doses of the suspected allergy culprit while under medical supervision -- called a food challenge -- is the gold standard for diagnosing food allergies, according to the researchers. The test directly measures whether a person develops an allergic reaction.

Tests like the skin prick, which puts a small amount of the allergen on the end of a needle while it pokes the skin, or a blood test measure antibodies that build up in the blood or around the prick site when a person is exposed to the allergen. But these tests do not measure the type of allergic reaction a person will get or how severe the reaction will be.

Previous research suggests that 8 percent of children will test positive for allergies on a skin or blood test, but only 1 percent will develop physical symptoms of an allergy.

Additional tests like a skin prick or blood test should only accompany the more reliable food challenge, the authors said.

"Allergy tests can help a clinician in making a diagnosis but tests by themselves are not diagnostic magic bullets or foolproof predictors of clinical disease," Dr. Robert Wood, allergist at Johns Hopkins Children's Center said in a statement. "Many children with positive test results do not have allergic symptoms, and some children with negative test results have allergies."