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The Overuse of Allergy Tests
A clinical report in the journal Pediatrics warns against overuse of allergy tests. Because positive tests offer only circumstantial evidence that a child has an allergy and false positives are common, unneeded allergy tests can end up doing more harm than good.
The report is designed to give pediatricians more guidance regarding when allergy testing is called for and when it isn't. The guidelines in the report will be useful for parents as well.
The purpose of an allergy test should be to help confirm a suspected allergy, not to look for an allergy in a person or child that doesn't show any symptoms of one. Allergy tests are simply one weapon in the arsenal used to find out if a suspected allergy exists. They should never be used as standalone evidence that a child has an allergy. Yet too often, they are.
For example, in children with moderate to severe asthma, an allergy test could be helpful. That's because asthma is often triggered by an allergy to cockroaches, pets, dust mites, pollen or other substances. But testing for an allergy to these substances in a child without any symptoms is basically a fishing expedition.
Most allergy tests look for production of specific antibodies after exposure to a substance like peanuts or pollen or dogs. Skin prick tests look for a swelling or weal after scratching a test substance onto the surface of the skin. Blood tests measure the amount of specific antibodies circulating in the blood after an injection of the suspect substance.
A positive test indicates a sensitivity to the test substance, that the substance does cause a reaction of the immune system. But an allergy is a much stronger reaction. More than just a sensitivity, it's a hypersensivity, an over-reaction to a substance. And neither skin prick tests nor blood tests can reveal if a person has an allergy
Allergies can have serious medical consequences. Sensitivity rarely has any consequences at all.
It does someone little good to find out that they're sensitive to peanuts, pets or pollen if it doesn't cause a medical problem. But it could cause people to lose a pet, avoid the outdoors or change their diet needlessly.
Allergy tests to peanuts turn up positive in up to 8% of children, yet only 1 in 8 children who test positive turn out to have a peanut allergy. It's a case where a little knowledge can do more harm than good.
Chronic rhinitis is another condition where children might benefit from an allergy test. Rhinitis is a catch-all term for irritation, swelling or congestion in the nose. Sometimes it's due to an allergy, sometimes it isn't. An allergy test can help point a finger at an allergic cause. But taking an allergy test simply to see if one is allergic to pollen isn't recommended.
Another drawback of allergy tests is that they can give false negatives as well as false positives. And while a strong positive reaction (large weal or very high blood antibody reading) is suggestive of an allergy, especially to foods, it shows no correlation with the magnitude of the possible allergic reaction — whether it would be a mild one or severe one.
For children who are suspected of having a food allergy, an oral food challenge, which tests for an actual allergic reaction, is a much more useful test than a skin prick or blood test.
The report authors offer a short list of recommended and non-recommended uses for allergy tests. And while the authors are mainly concerned with allergies in children, the list applies to adults as well.
The report appears in Pediatrics.
February 1, 2012