New Directions in Diagnostic Evaluation of Insect Allergy
New Directions in Diagnostic Evaluation of Insect Allergy
Diagnostic testing is centered on the demonstration of venom-specific IgE antibodies by skin test or serum test. As with all allergies, these tests are useful when they confirm a clear history of allergic reaction but have a poor overall positive predictive value. To understand this, we must recall that venom-specific IgE can be demonstrated in about 20% of normal adults, and up to 40% of those who have been recently stung. The presence of venom-specific IgE is not necessarily predictive of clinical reactivity or the severity of reaction to a sting. The risk of anaphylaxis to a future sting is predicted by many factors, including the history of reaction, the presence of venom-IgE, the natural history of the disease, the baseline level of mast cell mediators, and age. The demonstration of venom-IgE is associated with a modest chance of systemic reaction (10–15%) even in those with a negative history of sting reaction, and with a variable chance of systemic reaction in those with a positive history of allergic reaction, ranging from 5 to 75% depending on the severity of the prior reaction. The clinician often orders a test with the expectation that it will provide a clear direction for treatment and guidance of the patient. The test is, however, often being done after the fact (after an allergic reaction to a sting), with up to 40% chance of a positive result because of the sting itself. In most cases, we cannot know what the result would have been before the sting.
In a prospective sting challenge study, we found that the severity of the past sting reaction was correlated with the frequency, but not the severity, of systemic reaction to a sting. In this study, we also noted that the chance of systemic reaction was also correlated with the species of yellow jacket used for the sting challenge. This demonstrates that a patient could have no reaction to one yellow jacket sting, but could still have a severe reaction to another yellow jacket sting. The venom skin test also showed a correlation with the frequency of systemic reaction to sting challenge, with the lowest risk being in patients with negative venom skin test but positive venom-IgE.
Negative venom skin and serum tests have been reported in about 15% of patients with a convincing history of systemic reaction to a sting, some of whom will have systemic reactions to future stings. One effort to improve the sensitivity of skin tests was to dialyze the venom extract to eliminate small molecular weight components that cause nonspecific irritant reactions in the skin. This resulted in skin tests that detected 79% of the patients who had negative skin tests to commercial venom, some of whom also had negative serum tests. There remains a need to improve the sensitivity and specificity of diagnostic tests to predict systemic reactions to stings.
Current Venom Diagnostic Tests
Diagnostic testing is centered on the demonstration of venom-specific IgE antibodies by skin test or serum test. As with all allergies, these tests are useful when they confirm a clear history of allergic reaction but have a poor overall positive predictive value. To understand this, we must recall that venom-specific IgE can be demonstrated in about 20% of normal adults, and up to 40% of those who have been recently stung. The presence of venom-specific IgE is not necessarily predictive of clinical reactivity or the severity of reaction to a sting. The risk of anaphylaxis to a future sting is predicted by many factors, including the history of reaction, the presence of venom-IgE, the natural history of the disease, the baseline level of mast cell mediators, and age. The demonstration of venom-IgE is associated with a modest chance of systemic reaction (10–15%) even in those with a negative history of sting reaction, and with a variable chance of systemic reaction in those with a positive history of allergic reaction, ranging from 5 to 75% depending on the severity of the prior reaction. The clinician often orders a test with the expectation that it will provide a clear direction for treatment and guidance of the patient. The test is, however, often being done after the fact (after an allergic reaction to a sting), with up to 40% chance of a positive result because of the sting itself. In most cases, we cannot know what the result would have been before the sting.
In a prospective sting challenge study, we found that the severity of the past sting reaction was correlated with the frequency, but not the severity, of systemic reaction to a sting. In this study, we also noted that the chance of systemic reaction was also correlated with the species of yellow jacket used for the sting challenge. This demonstrates that a patient could have no reaction to one yellow jacket sting, but could still have a severe reaction to another yellow jacket sting. The venom skin test also showed a correlation with the frequency of systemic reaction to sting challenge, with the lowest risk being in patients with negative venom skin test but positive venom-IgE.
Negative venom skin and serum tests have been reported in about 15% of patients with a convincing history of systemic reaction to a sting, some of whom will have systemic reactions to future stings. One effort to improve the sensitivity of skin tests was to dialyze the venom extract to eliminate small molecular weight components that cause nonspecific irritant reactions in the skin. This resulted in skin tests that detected 79% of the patients who had negative skin tests to commercial venom, some of whom also had negative serum tests. There remains a need to improve the sensitivity and specificity of diagnostic tests to predict systemic reactions to stings.
Source...