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

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.

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.

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(R) (Los Angeles, USA) and Hycor HytecTM (Irvine, California, USA) methods. Each volunteer completed a questionnaire detailing latex exposure and allergic history.

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.

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.