Specific IgE levels in the diagnosis of immediate hypersensitivity to cows' milk protein in the infant

Background: A milk-free diet with substitute formula should be established when immediate symptomatic hypersensitivity to cows' mills protein (CMP) is diagnosed, and therefore an accurate diagnosis is very important. Objective: This study aims to find the optimal cutoff values for specific I gE antibody levels that discriminate between allergic and tolerant infants by using cows' milk and its principal proteins as allergens. Methods: A prospective study was carried out on 170 patients under 1 year o ld (mean, 4.8 months). These patients were seen consecutively over a 4-year period in our outpatient clinic and for the first time because of a reacti on suggesting immediate hypersensitivity after ingestion of cows' milk form ula. A clinical history, prick test with cows' milk and its proteins (alpha -lactalbumin, beta -lactoglobulin, and casein), determination of specific IgE antibodies with the CAP system FEIA for the same allergens as for the p rick test, and a challenge test according to the diagnostic protocol were p erformed in all of the children. A study of validity of the prick test (cut off point, 3 mm) and CAP system by using different cutoff points in the spe cific IgE, values for cows' milk and its proteins were also analyzed. Results: Prevalence of immediate symptomatic hypersensitivity to CMP in thi s study was 44%. When both the whole milk and its principal milk proteins w ere used in the prick test, the negative predictive value was very high, an d a negative value excluded allergy in 97% of the patients. When the differ ent cutoff points of the specific IgE for milk were analyzed, 2.5 KUA/L, ha d a positive predictive value of 90% and 5 KUA/L had a positive predictive value of 95%. Conclusions: When diagnosing immediate hypersensitivity to CMP in infants, negative skin test responses exclude allergy in most of the patients, if th e prick test response is positive, specific IgE levels for cows' milk may b e helpful. If these values are 2.5 KUA/L or greater, the challenge test sho uld not be performed because of its high positive predictive value (90%).