RATIONALE: Due to the lack of a FDA-approved skin testing reagent, diagnosis of latex allergy must rely on patient history and serologic assays. There has not been a recent large-scale study of skin and serologic testing in a low prevalence population to determine the PPV and NPV of serologic testing for latex allergy. METHODS: Health care workers underwent duplicate skin testing with Clone 600 extract and serologic testing for latex specific IgE measured by Pharmacia ImmunoCap. Sensitivity, specificity, PPV and NPV of the serologic assay were determined using skin prick testing as the gold standard for sensitization to latex. RESULTS: There were 792 paired skin and serologic tests. 40 skin tests were positive (5%). The sensitivity of the Pharmacia ImmunoCap assay was 35% and the specificity was 98%. The PPV was 48.3% while the NPV was 96.6%. There were 15 false positive serologic tests (1.9% of individuals tested) and 26 false negative tests (3.3%). CONCLUSIONS: Using an at risk population, with a 5% prevalence of latex allergy, we demonstrate that the performance of the FDA-cleared ImmunoCap serologic test for latex allergy has much lower sensitivity than previously reported. There were high rates of false positive and false negative results in relation to the prevalence of allergy in the population tested. This confirms suspicions that this serologic test should only be used for patients with a history of latex allergy and not used for screening the population with a low prevalence of latex sensitization.
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