Tuesday, January 24, 2012

Allergy Tests Should Only Verify Diagnosis in Children

From Medscape Education Clinical Briefs News Author: Ricki Lewis, PhD CME Author: Désirée Lie, MD, MSEd 01/10/2012 Clinical Context According to the current study by Sicherer and Wood, most allergic responses are mediated by immunoglobulin E (IgE) antibodies specific to the trigger allergen, which can be detected with in vitro or skin tests. Quantification of in vitro allergen-specific IgE (sIgE) levels is becoming more common. The 3 detection systems approved by the US Food and Drug Administration have excellent performance characteristics to identify different IgE antibodies but do not measure IgE antibodies with similar efficiencies. Therefore, a test for an allergen in 1 of 3 test systems may not be equivalent to the same allergen test in a different system. This is a review of different tests available for allergen testing in children and indications for use. Study Synopsis and Perspective Allergy tests should be used only to confirm a diagnosis that has already been made on the basis of symptoms and medical history, advise 2 leading allergists in an article published in the January issue of Pediatrics. Scott Sicherer, MD, from Mount Sinai Hospital in New York City, and Robert Wood, MD, from the Johns Hopkins Children's Center in Baltimore, Maryland, reviewed the benefits and limitations of blood tests and skin-prick tests in the detection of allergic diseases. For blood tests, enzymatic assays for IgE antibodies (in vitro sIgE) tests have replaced radioallergosorbent tests, but the 3 products approved by the US Food and Drug Administration either detect different antibody populations or do not measure them with comparable efficiencies. Both the skin-prick test (SPT) and sIgE test detect a sensitized state. "However, detection of sensitization to an allergen is not equivalent to a clinical diagnosis. In fact, many children with positive tests have no clinical illness when exposed to the allergen," Dr. Sicherer and Dr. Wood write. They further point out that testing for allergens that do not make sense (because they would never be encountered in the patient's environment or because the patient is obviously not allergic to them) could lead to "detrimental actions of unnecessary allergen avoidance." They also warn against a false-negative on an SPT or sIgE test when a child is obviously allergic to a particular trigger. The allergists identify circumstances in which SPT and sIgE are warranted: to confirm a suspected allergic trigger after observing a child react, to monitor the course of a food allergy to detect when it might be waning or outgrown, to confirm allergy to an insect after an anaphylactic response, and to identify allergies to vaccines (SPT only). SPT and sIgE tests should not be used, Dr. Sicherer and Dr. Wood write, to screen for allergies in nonsymptomatic children or to diagnose food allergies or drug allergies. Food allergies should be assessed with food challenges, they write, and skin and blood tests do not detect antibodies to drugs. The tests might be useful for identifying the trigger of a respiratory allergy (allergic asthma or seasonal or perennial allergic rhinitis) that is ubiquitous but not obvious in the patient's environment: for example, SPT or sIgE can detect allergy to dust mites, animal dander, cockroaches, molds, or pollen. The authors have disclosed no relevant financial relationships. Pediatrics. 2012;129:193-97. Abstract

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