The prevalence of children suspected of a cow's milk allergy is 17% in the Netherlands. Cow's milk diagnosis is based on a food challenge test However, this food challenge test is expensive, time consuming, risky, with waiting lists of several months. This waiting time results in unnecessarily long-term use of expensive hypoallergenic milk formula Therefore, there is a great need to introduce a better and faster diagnostic test for cow's milk allergy diagnosis in standard care. The in vitro Basophil Activation Test (BAT) is cheap, quick (result < 1 day, no waiting list), safe for the child and is a reliable alternative for the food challenge test to diagnose an IgE-mediated allergy. A diagnostic work-up with the BAT is expected to achieve a relevant reduction in the number of expensive and risky food challenges and the prescription of hypoallergenic formula. The reduction in diagnostic delay will increase quality of life.

Objective: Determination of the (cost)effectiveness of the replacement of the expensive, risky and time-consuming food challenge test by the Basophil Activation Test (BAT) for the diagnosis of an IgE-mediated cow's milk allergy in children.

Inclusion Criteria:

1. Age 0-12 years

2. Suspected of cow's milk allergy with one or more of the following complaints after intake of cow's milk:

   • angioedema
   • urticaria
   • sneezing and rhinitis <2 hours after feeding
   • sensation of swelling in the throat and/or difficulty swallowing <2 hours after feeding
   • voice change/hoarseness <2 hours after feeding
   • cough <2 hours after feeding
   • wheezing and/or shortness of breath <2 hours after feeding
   • loss of consciousness <2 hours after feeding
   • vomiting or abdominal pain or diarrhoea <2 hours after feeding in children <4 years only in combination with IgE-mediated complaints in other tracts

3. Placed on a waiting list for a hospital food challenge test

4. Blood draw for cow's milk sIgE and BAT < 3 months before the food challenge test. This blood draw will be simultaneously scheduled with a blood draw for regular diagnostics.

5. Signed informed consent parents/guardians

Exclusion Criteria:

1. Age > 12 years
2. Suspicion of Food Protein-Induced Enterocolitis Syndrome (FPIES)
3. Eosinophilic esophagitis due to a cow's milk allergy
4. Suspected cow's milk allergy <4 years with crying and/or agitation and/or eczema and/or abdominal pain and/or failure to thrive and/or blood loss per anum and/or diarrhoea and/or reflux and/or vomiting as the only manifestation of the allergy without IgE-mediated symptoms in another organ system
5. Systemic immunosuppressant use
6. Other underlying chronic conditions (immunological, oncological, chromosomal abnormalities).

Children suspected of an IgE-mediated cow's milk allergy and are eligible for a food challenge test at 2nd and 3rd line allergy centres.