Eligibility criteria
Prospective, retrospective, cross-sectional, and case-control studies were included in our study examining CRD in the diagnosis of milk allergy in children or adults. Studies needed to include sIgE measured for at least one milk allergen component (Bos d 4, 5, 6, 8) and provide sufficient data to calculate the following four relevant diagnostic indices: sensitivity, specificity, PPV, and NPV. Oral food challenge (double-blind or open) was the reference standard, and at least 50% of patients received OFC. We excluded secondary studies (e.g., reviews or systematic reviews), case reports, and animal studies. Only full-text available articles were included.