Patient testing

Patient testing should include sensitivities to rubber additives and allergic reactions to latex proteins.

Rubber additives

Patients with hand dermatitis and exposure to latex should be referred for consultation to determine and document sensitivities to rubber additives. Patch testing is the diagnostic method for allergen identification in allergic contact, but not irritant dermatitis. In patch testing, immunogenic rubber additive chemicals of appropriate concentration are taped onto the patient's back for 48-96 hours. Patch tests are performed and interpreted according to standardised techniques.

All exposed patients with hand dermatitis should also be referred to an allergy specialist to determine if they possess IgE antibody to latex proteins.

Skin tests

Presently, skin testing with allergen extracts is the most sensitive means of detecting IgE antibody.

Skin testing extracts to determine latex protein allergy have included commercial extracts, latex glove extracts and hevea leaves. No standardised latex extract is presently available.
 
Because of the potential for serious anaphylactic reactions, skin testing must be done by qualified specialists with full resuscitative equipment and medication available in the event of reactions to the testing material.

In vitro tests

In vitro tests measure the IgE response in the serum of a latex-allergic patient. Analysis of the latex proteins has determined that there are over 240 such proteins, and anti-IgE antibody testing has shown that 25% are associated with the allergic response. Latex IgE-binding proteins vary in size and appear to differ between patient groups. Spina bifida patients have IgE antibodies to a 27 kD peptide, whereas healthcare workers may produce IgE antibodies to a 20 kD peptide. Research is ongoing in the characterisation of these proteins, with the goal of modifying or reducing the offending allergens.

In vitro testing should be carried out in the following circumstances:

• to confirm results of skin testing
• when skin testing is considered too dangerous to perform
• when skin testing is not available

In vitro immunoassays are designed to measure IgE antibody in serum. Several research and clinical latex-specific IgE assay methods are currently used, including the enzyme-linked immunosorbent assay (ELISA), the radioallergosorbent test (RAST) and ImmunoCAP System (Upjohn-Pharmacia, Uppsala, Sweden), and the latex AlaSTAT (Diagnostic Products Corporation, Los Angeles, CA, USA). In addition, other research procedures, such as Western blot analysis, have been useful in identifying and characterising the molecular weights of allergenic latex proteins. In early studies, the RAST displayed a 53% diagnostic sensitivity as compared with skin tests with latex extracts. Since then, more recent studies have shown that research assays and clinical tests, such as the AlaSTAT, have increased the sensitivity of allergic skin testing. In one study, this diagnostic sensitivity approached 96% in comparison to skin testing. Both skin testing and in vitro assays detect the presence of a latex-specific IgE antibody in the skin and serum, respectively, and do not necessarily predict clinical presentations such as anaphylaxis.