We have received a number of calls from practitioners asking whether a negative result on a serum allergy test justifies exposure to a food (i.e. peanuts) that has caused a severe (i.e. anaphylactic) reaction in a patient in the past. Recent research has demonstrated conclusively that serum and/or skin prick tests do not reliably predict whether a patient can safely be exposed to a food that has caused a severe reaction in the past.
A study of 1000 patients with peanut and/or nut allergies, from the University of Cambridge Clinical School, concluded that the magnitude of skin prick test or serum IgE test result does not predict clinical severity, with no difference in median test results between patients with minor urticaria and patients with anaphylaxis. 22% of negative serum IgE tests were falsely reassuring. The authors concluded that, “these tests cannot be interpreted in isolation and that detailed clinical history is essential.” (Clin Exp Allergy 2003;33:1041) A review published inPostgraduate Medicine in 2001 makes the same point (see below).
The serum allergy tests offered by Meridian Valley Laboratory were developed to identify foods causing delayed hypersensitivity, food intolerance-type reactions. Practitioners use them to help patients avoid foods that aggravate chronic health problems, such as sinusitis, ear infections, etc. Evaluation of severe, immediate hypersensitivity reactions to foods, including anaphylaxis, should be based on patient history, not serum allergy tests.
In the interest of patient safety, we have added the following warning to our allergy reports. We recommend that clinicians routinely discuss this warning with patients as part of their review of allergy test results.
NEW WARNING ON MVL ALLERGY REPORTS
A negative in vitro allergen-specific IgE antibody test should not be used to justify exposure to an allergen that is clinically suspected as the cause of an anaphylactic reaction.
- POSTGRADUATE MEDICINE /VOL 109 / NO 5 / MAY 2001
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