Background: IgE-mediated cow's milk proteins (CMPs) allergy shows a tendency to disappear with age. The sooner tolerance is detected, the earlier the substitute diets can be suspended and the quicker family emotional hardship is alleviated.
Objective: To analyse the specific IgE levels to cow's milk and its proteins, which help to separate tolerant from no tolerant children in the follow-up of infants with allergy to cow's milk.
Patients and methods: Sixty-six infants diagnosed with IgE-mediated allergy to CMPs were included in this prospective follow-up study. Periodic reassessments were carried out every 6 months until they were 2-years old and then, annually, until tolerance arose or until the last reassessment in which tolerance had not been achieved. Non-tolerant infants were followed, at least, for a period of 3 years. In each visit, the same skin tests and determination of specific IgE (CAP System FEIA) for milk and its proteins were carried out. The open challenge test was repeated unless a clear transgression to milk, which came to be positive, had taken place within the previous 3 months in each of the follow-up visits. Specific IgE levels to milk and its proteins, in different moments of the follow-up were analysed by means of the receiver-operating characteristic curve to predict clinical reactivity.
Results: Throughout the follow-up 45 (68%) infants became tolerant. The follow-up mean for tolerant infants was 21.2 months whereas for non-tolerant infants it was 58 months. The specific IgE levels which were predictors of the clinical reactivity (positive predictive value (PPV)> or =90%), grew as the age of the infants increased: 1.5, 6 and 14 kU(A)/L for milk in the age range 13-18 and 19-24 months and in the third year, respectively. Specific IgE levels to casein: 0.6, 3 and 5 kU(A)/L, respectively, predicted clinical reactivity (PPV> or =90%) in the different analysed moments of the follow-up. The cut-off points: 2.7, 9 and 24 kU(A)/L for milk and 2, 4.2 and 9 kU(A)/L for casein, respectively, predicted clinical reactivity with an accuracy > or =95% corresponding to a specificity of 90%.
Conclusions: Monitorization of specific IgE concentration for milk and casein by means of the CAP system in allergic children to CMPs allows us to predict, to a high degree of probability, clinical reactivity. Age factor must be taken into account to evaluate the specific IgE levels which are predictors of tolerance or clinical reactivity.