At this time, there are three methods by which allergy to venom from stinging insects can be assessed: (1) determination of the clinical severity of the reaction, (2) skin tests to measure reactivity, and (3) RAST or CAP System assay to measure specific IgE. From a linear thinking perspective, it might be assumed (excluding loss of reactivity with time as a factor) that a correlation exists between these three parameters; this does not, however, appear to be the case.
Patrizzi and colleagues evaluated skin tests and estimations of specific IgE antibodies by RAST in patients with bee-sting allergy [7]. The results corresponded in 82% of the patients. Hoffman compared RAST and skin test results for five venoms in 60 patients with histories of stinging-insect allergy; 48 patients with positive skin test results showed an 88% correlation of RAST and skin test scores [8]. Egner and colleagues reported that the level of IgE antibody to venom does not reliably reflect the severity of the last reaction to a sting in patients with double positive reactivity to stings both from honeybees and from Vespula species [9].
Mosbech, in a comparative study of venom-allergic patients, found a positive correlation (p < .05) between the results of skin-prick tests and specific IgE against venoms. For patients allergic to yellowjacket stings, there was also a correlation between the severity of symptoms after the sting and the size of the skin-prick test reaction to venom [2]. In contrast, Nittner-Marszalska and colleagues found that for patients with allergy to the venom of insects of the order Hymenoptera, there was no correlation between the size of the skin test reaction, the class of venom-specific IgE level (by fluorescent allergosorbent technique [FAST]), and the results of basophil histamine release. In addition, no relation was found between the results of these tests and the severity of the sting reactions as measured on the Mueller scale [3].
In this analysis of 36 patients with immediate hypersensitivity reactions to stinging-insect venoms, no correlation was found between the degree of skin test reactivity or RAST score and the severity of the clinical reaction. The absence of a significant correlation persisted when individuals who were assessed more than 12 months after their clinical reaction were excluded from the analysis. A correlation was found between the degree of skin test reactivity and venom-specific IgE levels measured by RAST.
The fact that skin test reactivity and specific IgE levels measured by RAST are not predictors of the clinical severity of a reaction is apparently not unique to venom allergy. Rosario and Vilela found that when using quantitative skin-prick tests with an average endpoint allergen concentration of 50 allergen units (AU) on atopic asthmatic patients, the mean wheal diameter was not significantly greater for severely asthmatic patients than for mildly asthmatic patients [4]. In patients with nut allergy, Clark and Ewan [5] found no correlation between skin-prick test wheal size and the graded severity of the worst reaction for all nuts combined or for peanut, hazelnut, almond, and walnut. For the CAP System specific IgE levels, there was no correlation for all nuts, so the size of SPT or CAP System levels did not predict between minor urticaria and anaphylaxis.
These results indicate that specific IgE level as assessed by either skin testing or serum IgE is only one determining parameter in the induction of anaphylaxis and that other factors must play a role. Such factors could be mast-cell mass, mast-cell stability, concomitant medications, number of stings or amount of venom injected, and levels of blocking antibodies. Although it is tempting to assume so, the size of the skin test reaction to an allergen or the level of specific IgE does not necessarily predict clinical reactivity.
In contrast to the above studies, Souille and colleagues [1] assessed 59 asthmatic children by skin-prick tests, RAST (specific IgE), and bronchial provocation with common inhalants. They found a significant connection between the results of the three tests. However, the concordance level was only moderate, i.e., not greater than 68%. In comparison with bronchial provocation, prick testing and RAST respectively yielded numerous false-positive and false-negative results. This is perhaps not surprising, given the problem of allergen sensitization without clinical reactivity and the reduced sensitivity of RAST when compared with skin testing. In this study, the negative predictive value of skin-prick tests was considered satisfactory, and the most discriminatory threshold for the positive RAST result was the class-3 response. This would suggest that correlation between the magnitude of skin-prick tests or RAST and bronchial challenge was not good.
van der Linden and colleagues reported on insect-sting challenge of 324 subjects with a previous anaphylactic reaction to yellowjacket and honeybee stings and found that a recurrence of anaphylaxis was observed in 25% of those sensitive to yellowjacket stings and 52% of those sensitive to honeybee stings [10]. Even more striking were the findings of van Halteren and colleagues, who described 348 patients with a previous history of anaphylaxis to stings and with mild or no symptoms on in-hospital sting challenge; 129 of these subjects subsequently were accidentally stung in the field, and 110 had only local reactions whereas 6 patients experienced serious manifestations [11]. Therefore, previous history of a severe response to a sting is not predictive of a subsequent serious reaction to accidental sting challenge. Meanwhile, two-thirds of individuals who die from a sting reaction have no previous history of their allergy [12].
