Understanding Latex Allergy
in the Healthcare Setting

METHODS USED FOR THE ESTIMATION OF THE PROTEIN CONTENT AND/OR ALLERGENICITY OF NATURAL RUBBER LATEX PRODUCTS   Modified Lowry Assay (ASTM method D 5712-99) Elisa Assay (ASTM method D 6499-00) INDICATIONS Tests for the amount of total water-extractable protein associated with NRL and its products. Tests for residual protein content in NRL material such as gloves. Measurement of total latex protein and, more importantly, immunologically reactive latex protein. METHODOLOGY Dye-binding test. Residual water-soluble proteins are extracted in accordance with ASTM method D 5712 at a temperature of 37 ± 2°C, then precipitated to remove interfering water-soluble substances. It is calibrated to measure at a minimum of 50 micrograms/gram NRL. The protein content is then determined by the Lowry method of protein analysis, using a protein standard. The FDA mandates this as the measurement technique for total protein content. The FDA has stated that the lowest claim that can be made is as follows: “This latex glove contains 50 micrograms or less of total water-extractable protein per gram.” No one is allowed to claim a lower protein content. Indirect ELISA colorimetric technique in which latex proteins are immobilized by adsorption to plastic and reacted with rabbit anti-latex antisera. After washing, the plate is reacted with a second HRP-labeled, anti-rabbit IgG and, finally, a substrate is added that results in a color change. The spectro-photometric absorbance of the orangecolored reaction product is measured at 492nm. RESULTS Protein content will be measured in a range from microgram to milligram quantities. This assay can easily detect latex proteins in extract solutions and is sensitive to 15 ng/ml (1 ng = 10-9 g). ADVANTAGES An inexpensive test, rapid and easily performed. Allows for alterations of chemical impediment. Test is very sensitive and reproducible. Specific for latex protein and immunologically reactive protein, making it relevant for latex allergy. Does not utilize radioisotopes and is therefore easy to use. Can be performed as an ELISA Inhibition Assay. DISADVANTAGES A large number of substances often added to NRL during compounding can cause interference to these assays. Limited sensitivity. Lack of specificity. Erroneous results can occur due to the complex mixture of polypeptides in the latex. No certified standard reference material is currently available to assess the accuracy of this test method. Uses latex proteins extracted from non-compounded ammoniated latex films. Uses rabbit, rather than human, sera. Has not been validated against specific allergenmeasuring methods, such as SPT or RAST Inhibition. It is important to understand that all of these tests are not 100% accurate; testing methods continue to evolve. It is also vital to remember that over 240 proteins have been identified in latex, with about 50 of them being allergenic. Only 13 proteins in NRL (Hevea brasiliensis [Hev b]) that bind human IgE have been isolated and characterized as Hev b allergens by the International Nomenclature Committee of Allergens (http://www.allergen.org [accessed May 7, 2006]). Research has shown that the reduction of residual extractable proteins in latex gloves has a significant impact on reducing the incidence of allergic reactions to latex. Recent studies in the U.S., Canada, and Europe demonstrate that wearing lowprotein, powder-free latex gloves greatly reduces the risk of allergic reactions and the likelihood of developing latex sensitivity. In addition, studies have shown that the use of low-protein, powder-free gloves allowed latex-sensitive individuals donning synthetic gloves to work safely alongside their colleagues. The National Institute for Occupational Safety and Health (NIOSH) now recommends using powder-free, low-protein latex gloves. The Association of periOperative Registered Nurses (AORN) and the American Nurses Association, as well as other industry organizations, also now recommend powder-free gloves with low protein content (consistently below 50 ìg/g). When testing comparisons are made, it is imperative to recognize that each testing method is unique. When comparing testing results, it is essential to compare results from the same testing method. It is vital to keep in mind the FDA statement in a March 1995 Citation, titled FDA March 1995 interim guidance on protein content of latex medical gloves: “Although there are insufficient clinical data to set a protein level that dramatically reduces the incidence of reactions to latex protein, there is scientific consensus that reduced protein levels will lower the potential for both sensitization of non-sensitized individuals and allergic reactions in sensitized individuals.” The FDA mandates that manufacturers who include total extractable protein figures also include this statement: “Caution: Safe use of this glove by or on latex-sensitized individuals has not been established.” The FDA prohibits products to be labeled with total extractable protein levels lower than 50 micrograms per gram, as this is the sensitivity limit of the ASTM Lowry test method.

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