Whey and casein specific IgE and the cow's milk challenge test for atopic children.

We studied 30 atopic children who suspected of milk allergy by past history (age ranging from 1 yr 4 mo to 9 yr 6 mo, mean age: 5.03 yr.) diagnosed as having asthma, atopic dermatitis and/or allergic rhinitis. These 30 atopic children had been screened from the patients at our outpatient clinic by the Pharmacia CAP system RAST FEIA. All of them showed the presence of at least Class II (greater than 0.7 ku/l) IgE specific to proteins in cow's milk. Further analysis found IgE specific to alpha-lactoalbumin (alpha-LA) elevated in 1 patient (3.3%), 1 patient (3.3%) to beta-lactoglobulin (beta-LG), 4 patients (13.3%) to alpha-LA and beta-LG, 5 patients (16.7%) to casein, 8 patients (26.7%) to casein and alpha-LA, 11 patients (36.7%) to casein, alpha-LA and beta-LG. After 3 weeks' cow-milk-free diet, the patient's milk challenge test was performed at our outpatient clinic. According to the test result, none of these 30 atopic children showed clinical evidence of significant allergic reaction to cow's milk in the skin, the gastrointestinal tract or the respiratory tract either within two hours after the challenge test or within 3 days after they went home. We therefore conclude that: (1) No single major allergen is apparent in cow's milk: casein, alpha-LA and beta-LG all show a high proportion of positive reaction. (2) Many atopic children fully tolerate cow's milk, although they have high titer of IgE antibodies specific to cow's milk. The RAST test is only the first step to screen patients with suspected IgE-mediated allergies. To make sure, any positive reaction must be confirmed by the "golden standard" for diagnosis, i.e., the double-blind placebo-controlled food challenge.