Assessment of latex allergy in a healthcare population: are the available tests valid?

Background Latex allergy can cause serious, preventable work-related health problems in healthcare workers who are a high risk group for this form of allergy. Type I hypersensitivity can produce life-threatening systemic effe cts, and involves an allergen-specific immunoglobulin (IgE) response to pro teins found in latex. The estimated prevalence of latex 'allergy' in health care workers varies widely (2.8% - 18%), and studies do not always distingu ish between those who are positive in an assay for latex-specific IgE and t hose with clinical allergy. Objective To assess the performance of four in-vitro methods and three skin testing methods for detecting latex-specific IgE in a group of UK healthca re workers. Test results were compared with reported clinical symptoms defi ned by questionnaire. Methods Skin prick testing was carried out on volunteers using three reagen ts: (a) stallergenes commercial latex extract (Cedex, France); (b) an in-ho use latex glove extract; and (c) a fresh glove piece. Specific IgE levels w ere determined using Pharmacia Autocap(TM) (Uppsala, Sweden), Pharmacia Uni cap(TM) (Uppsala, Sweden), DPC Immulite(R) (Los Angeles, USA) and Hycor Hyt ec(TM) (Irvine, California, USA) methods. Each volunteer completed a questi onnaire detailing latex exposure and allergic history. Results In vitro methods for detecting specific IgE to natural rubber latex were positive in 3.6%, to 43.6% of the same population. Skin prick tests p ositivity varied between 2.9% and 14.3% with different extracts. From the s ubjects tested 9.1% reported symptoms which could be consistent with type I allergy, although none had been given a pre-existing diagnosis of latex al lergy, and 43.6% of volunteers reported symptoms consistent with type IV hy persensitivity or irritant dermatitis. Contingency tables and chi-squared analysis revealed no correlation between most methods. No correlation was shown between symptoms consistent with ty pe I allergy and any in vitro or skin testing method for latex-specific IgE . Conclusions A wide variation between testing procedures was found, and no m ethod could be correlated with reported symptoms of type I allergy. At leas t one in vitro specific IgE assay produced a high percentage of positive re sults at variance with the clinical symptoms in volunteers. A clinical hist ory is essential in establishing type I hypersensitivity to latex and test results should not be used in isolation. The incidence of clinical sensitiz ation may be seriously over-estimated if only laboratory parameters are use d.