Blood tests and skin prick tests should never be used to make a standalone allergy diagnosis, two doctors have warned.
Professor Robert Wood, of the Johns Hopkins Children’s Centre, Baltimore, Maryland, and Dr Scott Sicherer of Mt. Sinai Hospital in New York, said clinicians should proceed with caution when ordering allergy tests.
Instead of using them to diagnose allergies, the tests should be used only to confirm suspicion.
Writing in the January edition of Pediatrics, Professor Wood and Dr Sicherer say that test results should be looked at in conjunction with a patient’s symptoms and medical history.
If a food allergy is suspected, patients should undergo a food challenge, which involves consuming small doses of the suspected allergen under medical supervision.
“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,” Prof Wood says. “Many children with positive tests results do not have allergic symptoms and some children with negative test results have allergies.”
Skin tests and blood tests are proxies that detect the presence of immunoglobulin (IgE) antibodies, immune-system chemicals released in response to allergens that can tell if someone is sensitive to a particular substance but cannot reliably predict if a patient will have an actual allergic reaction.
However, many people who have positive skin tests or measurably elevated IgE antibodies do not have allergies.
Physicians should also caution against comparing results from different tests and laboratories because commercial tests vary in sensitivity.
Prof Wood and Dr Sicherer say blood and skin tests should be used to confirm a suspected allergic trigger after observing clinical reactions; monitor the course of established food allergies via periodic testing; confirm an allergy to insect venom following a sting that causes anaphylaxis; and to determine vaccine allergies.
However, they should not be used as general screens to look for allergies in symptom-free children or to test for drug allergies.
Pediatrics January 2012
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