Childhood Allergy

• In children, who should be tested?

• At what age can a patient be tested? Can I order this test for an infant?

• What if a child with skin or GI symptoms tests positive for several foods?

• How do I use this information to avoid eliminating too many foods from the diet?

• How much blood is needed for the test?

In children, who should be tested?

A: While a child presenting with allergy-like symptoms is a candidate for specific IgE testing, it is not likely that every child with a rash or rhinorrhea needs the test. Nevertheless, I don’t hesitate to test when it feels appropriate. I employ ImmunoCAP Specific IgE blood testing in accordance with the guidelines published by the European Academy of Allergy and Clinical Immunology, which recommends allergy testing for children with allergy-like symptoms deemed to be persistent, recurrent, or severe, or for those in need of continuous treatment for a particular illness, regardless of the age of the child. In addition, allergic sensitivities may shift over time. In the Allergy March, a child can present with symptoms of common illnesses that manifest from low-level food sensitivities and mild inflammation, such as atopic dermatitis or gastrointestinal complaints. Later on, he or she may become sensitive to inhalants, which may cause recurring acute otitis media or allergic rhinitis. Allergy March illnesses progress in severity and often result in allergic asthma. Because of these shifting sensitivities, I sometimes repeat the test to assess the progression of the allergic sensitivities and see if there have been any shifts between foods and inhalants, and indoor and outdoor allergens.

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At what age can a patient be tested? Can I order this test for an infant?

A: This test may be run on patients 3 months of age or older.

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What if a child with skin or GI symptoms tests positive for several foods?

A: Positive allergy test results must be correlated clinically with signs and symptoms of disease.  Many children (and adults) may have low levels of IgE present against specific foods that they consume seemingly without difficulty.  Alternatively if there are typical clinical signs and symptoms following the ingestion of a food in question, an elevated specific IgE toward that food warrants a trial of dietary elimination.

If a clinician does not feel comfortable performing a detailed food evaluation or elimination diet, then I would recommend that he or she go ahead and refer the patient to an allergist. If your patient’s test report shows multiple food sensitivities and you feel comfortable following through on managing them, you can simply focus on the food with the highest reported specific IgE level. Educate and counsel the patient’s parents to eliminate that one food from the child’s diet. Follow up in 2 to 3 weeks to see if symptoms have resolved or improved. If not, rotate the diet by counseling elimination of the food that registers the next highest level of specific IgE and adding the previous food back to the patient’s diet. I want to stress here that patients showing even low-level reactivity to anaphylaxis-prone allergens (eg, peanuts, tree nuts, and shellfish) should be referred directly to an allergist for further evaluation.

One other important point is that there is a small percentage of food allergy that is cell-mediated. Neither skin-prick test nor IgE measurement is capable of detecting this sensitivity. History supplemented by (double-blind placebo-controlled) oral food challenge is useful in this small group of patients.

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How do I use this information to avoid eliminating too many foods from the diet?

A: A test report on the ImmunoCAP multi-allergen childhood allergy panel offers detailed information to guide a cautious rotational elimination diet. The specific IgE measurements are extremely helpful to avoid unnecessary dietary restriction or changes.  In cases of food allergy among children with atopic dermatitis, cutoff values for IgE antibody concentrations to egg, milk, peanuts, and fish have been derived to provide 95% positive and 90% negative predictive values. See published work by Sampson and Ho in J Allergy Clin Immunol. 1997 Oct;100(4):444-51.

I want to stress that, if a clinician does not feel comfortable performing a detailed food evaluation or elimination diet, then I would recommend that he or she go ahead and refer the patient to an allergist. If your patient’s test report shows multiple food sensitivities and you feel comfortable following through on managing them, you can simply focus on the food with the highest reported specific IgE level. Counsel the patient’s parents to eliminate that one food from the child’s diet. Follow up in 2 to 3 weeks to see if symptoms have resolved or improved. If not, rotate the diet by counseling elimination of the food that registers the next highest level of specific IgE and adding the previous food back to the patient’s diet. I want to stress here that patients showing even low-level reactivity to anaphylaxis-prone allergens (eg, peanuts, tree nuts, and shellfish) should be referred directly to an allergist for further evaluation.

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How much blood is needed for the test?

A: All it takes is a single blood sample. 40 microliters + dead volume is usually needed per allergen, so 1 serum separator tube or spun barrier tube (red top) is required for a panel of allergens. EDTA plasma may also be used (ImmunoCAP Specific IgE procedure). Specimens should ship at room temperature and they can be stored at 2° to 8°C for up to 1 week. Please contact your laboratory to determine the exact quantity of sample they require per test.

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