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

Authors


W.Egner Department of Immunology, Northern General Hospital, Herries Road, Sheffield, S5 7YT, UK.

Abstract

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 effects, and involves an allergen-specific immunoglobulin (IgE) response to proteins found in latex. The estimated prevalence of latex ‘allergy’ in healthcare workers varies widely (2.8% − 18%), and studies do not always distinguish between those who are positive in an assay for latex-specific IgE and those 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 healthcare workers. Test results were compared with reported clinical symptoms defined by questionnaire.

Methods

Skin prick testing was carried out on volunteers using three reagents: (a) stallergenes commercial latex extract (Cedex, France); (b) an in-house latex glove extract; and (c) a fresh glove piece. Specific IgE levels were determined using Pharmacia AutocapTM (Uppsala, Sweden), Pharmacia UnicapTM (Uppsala, Sweden), DPC Immulite® (Los Angeles, USA) and Hycor HytecTM (Irvine, California, USA) methods. Each volunteer completed a questionnaire 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 positivity varied between 2.9% and 14.3% with different extracts. From the subjects tested 9.1% reported symptoms which could be consistent with type I allergy, although none had been given a pre-existing diagnosis of latex allergy, and 43.6% of volunteers reported symptoms consistent with type IV hypersensitivity or irritant dermatitis. Contingency tables and chi-squared analysis revealed no correlation between most methods. No correlation was shown between symptoms consistent with type 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 method could be correlated with reported symptoms of type I allergy. At least one in vitro specific IgE assay produced a high percentage of positive results at variance with the clinical symptoms in volunteers. A clinical history is essential in establishing type I hypersensitivity to latex and test results should not be used in isolation. The incidence of clinical sensitization may be seriously over-estimated if only laboratory parameters are used.

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