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 eight percent of children, yet only one in eight 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 a 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.
- To help confirm a suspected allergy after observing possible symptoms of one (asthma, rhinitis, severe reaction to an insect sting).
- To monitor the course of a known food allergy over time. The results of periodic allergy tests can help show if a child remains allergic to a substance or is becoming less allergic and is possibly outgrowing the allergy.
- To help determine if allergies suspected to have been caused by a vaccine were actually due to that vaccine.
- As general screens to look for allergies in symptom-free children.
- To test for drug allergies (these rarely come up positive, even if an allergy exists).
The report appears in Pediatrics.
This article originally appeared on TheDoctorWillSeeYouNow.com, an Atlantic partner site.