Cow’s milk casein, a hidden allergen in natural rubber latex gloves

Background: We have previously noted that one natural rubber latex (NRL) glove brand used for skin prick testing in the diagnosis of NRL allergy contained cow’s milk casein. Objective: We sought to examine whether other commonly marketed NRL glove brands contain cow’s milk casein. Methods: The casein content of 30 NRL glove extracts (1:5 wt/vol) was measured by RAST inhibition and by rocket immunoelectrophoresis and rocket radioimmunoelectrophoresis by using casein-specific rabbit antiserum, a serum pool from patients with cow’s milk allergy, and radiolabeled anti-human IgE. The NRL allergen content was measured by ELISA inhibition. Results: The casein content of the glove used in NRL allergy screening (Triflex, Baxter) was rather high (ie, about 400 μg/g of glove). Its total protein content was 1000 μg/g of glove. Rocket radioimmunoelectrophoresis detected distinct amounts of casein in 8, minimal amounts in 7, and no casein in the remaining 15 NRL glove brands. Conclusions: Several brands of NRL gloves were found to contain casein, implying that extracts prepared from such gloves can cause false-positive skin prick test reactions when diagnosing NRL allergy. The use of casein as a stabilizer in glove manufacture without appropriate labeling should be stopped because it can also cause contact urticaria syndrome in individuals with cow’s milk allergy. (J Allergy Clin Immunol 1999;104:177-80.)