The ASTM Standards for Determining Extractable Protein Levels From Natural Rubber Latex (NRL) Products

There are currently three ASTM standards used to quantify extractable NRL proteins. The first standard adopted in 1995, ASTM D5712, is a chemically based assay that quantifies total protein levels. This standard is a modification of the Lowry assay and may be susceptible to interference from chemicals used in the manufacturing process. The assay quantifies the total amount of protein whether it is derived from Hevea, the product of contamination (bacterial), or directly introduced during the manufacturing process such as casein, or enzymes. This lack of specificity is both a strength and weakness of the assay. FDA labeling claims are based on the D5712 assay results.

There are two immunologically based methods where antibodies are used to quantify antigenic (ASTM D 6499) and allergenic (ASTM D7427) protein levels. The D6499 standard uses polyclonal rabbit antibodies, while the D7427 standard uses monoclonal antibodies directed against four specific NRL allergens. These assays are less susceptible to chemical interferences, have much lower detection limits than the D5712, and are specific for Hevea proteins. Results from the D6499 assay are used in support of Latex Free claims. A survey of gloves on the market led to the recommendation of a maximal protein limit. Since the adoption of these limits the level of extractable protein in gloves has dropped and new cases of allergy and sensitization have also declined.