Performance of the Basophil Activation Test in the Diagnosis of IgE-mediated Cow's Milk Allergy in Infants and Evaluation of Hydrolysate Allergenicity.

The goal of this clinical trial is to investigate if the basophil activation test (BAT) represents a safer, faster, and more cost-effective diagnostic modality than the state-of-the art diagnostic work-up (specifik IgE and oral food provocation test) in infants with a suspicion of milk allergy. The main questions it aims to answer are: 1. If the BAT has superior diagnostic specificity compared to sIgE alone when diagnosing milk allergy 2. If the BAT is able to measure the allergenicity of hydrolysates 3. If implementing the BAT in the diagnostic work-up of milk allergy will be cost-effective by reducing in-hospital food challenges 4. If QoL is higher after an OFC compared with before the OFC, irrespective of the outcome of the OFC Participants who undergo usual asessment for milk allergy (that is IgE measurement in blood and oral food provocation) will be asked to 1. deliver blood for BAT (extra 3 ml when blood for IgE measurement is drawn) 2. The parents will be asked to fullfill a QoL questionnaire

Inclusion Criteria: 1. Age: less than 4 years 2. History of Type 1 milk allergy 3. Clinically indicated for diagnostic work-up of cow's milk allergy involving blood sampling (sIgE) and scheduled in-hospital oral food challenge test d Signed informed consent from parent(s) / legal guardian(s). Exclusion Criteria: 1. Children who previously have underwent an OFC for milk 2. Children who have received biological treatment or systemic steroids