How does the doc know that the patient is allergic or intolerant to dairy? what tests are done?

Skin test/blood test: In milk allergy, the symptoms include gastrointestinal upset, nasal stuffiness, hives, +/- anaphylaxis. In dairy intolerance, the symptoms will mostly be gastrointestinal. Blacks often have intolerance to lactose -in which you would have gas +/- diarrhea after eating dairy products because of an enzyme deficiency. Skin or blood test helps to confirm or rule out the presence of allergy.