10/15/03 Negative venom skin tests in individuals with previous systemic reactions to hymenoptera stingsSummaryThe presence of a positive intradermal skin test to low concentrations (< 1 mcg/ml) of venom extracts from one or more hymenoptera insects (honeybee, wasp, hornet, yellow jackets) has been considered a requisite for diagnosing systemic allergic reactivity to such venoms. However, some individuals with convincing histories of systemic reactions to a previous sting from such insects have negative venom skin test responses, even when such tests were carried out at least 4-6 weeks after the reaction (to avoid a possible refractory period). The usual practice has been to tell such "history-positive/skin test negative" patients that either: 1) their previous reactions were not truly allergic (toxic, psychologic?) or 2) if they had allergic but this allergy has waned. Venom immunotherapy was not recommended if the skin test was negative even if the previous reaction sounded quite severe. Now in a Rostrum article in the JACI, Golden and other members of the Insect Committee of the AAAAI have concluded that these clinical guidelines about venom hypersensitivity need re-evaluation. They point out that in vitro tests for IgE anti-venom antibodies are usually not requested when the venom skin tests are negative in a patient because of the general impression that the skin tests are more sensitive than in vitro tests for detecting IgE anti-venom antibodies. It is certainly true that in vitro tests for such antibodies may be negative in about 20% of those with positive venom skin tests. However, what is less well known is that about 10-12% of individuals with IgE anti-venom antibodies detected in vitro have negative venom skin tests. In some of these cases, the levels of IgE antibodies are not elevated by much. However, it is clear that the level of IgE anti-venom antibodies detected by current in vitro techniques does not correlate well with the severity of the previous sting reaction(s) described by the patient. Then what is the clinician to do? The authors recommend obtaining an in vitro test for anti-venom antibodies if the described previous reaction sounds highly suggestive of an allergic reaction and the venom skin test is negative. If levels of anti-venom antibodies are increased in the in vitro test, the patient should be considered systemically allergy and therefore instructed carefully in avoidance measures, carrying/use of self-injectable epinephrine (Epi-Pen) and venom immunotherapy, if indicated. Although some individuals without true systemic venom allergy may be mis-labeled with this approach, the author felt it better to err on the side of safety because of the potential for life-threatening sting reactions. Reference J Allergy Clin Immunol 2003; 112:495-8 Editor's Comments This discussion and associated recommendations "shakes up" some of the existent thinking about hymenoptera sting reactions. Golden has been one of the leading clinical investigators of venom allergy. His recommendation about use of in vitro tests is based on the availability of a high quality immunology lab in Johns Hopkins. However, one may not have the same degree of reliability in all the commercial labs performing this type of assay (and the particular lab chosen sometimes dictated by the patients HMO). Golden states that there is variability among results from different commercial labs. Obviously, lab approaches with better sensitivity/specificity profiles are needed.
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