Thus the parents careful description of what happens with different foods can be helpful. Skin tests and blood tests to measure the body's degree of sensitivity can be helpful for foods such as cow milk, egg, peanut, nuts and fish. A very large skin test reaction can be diagnostic, These tests can identify nearly half the children with allergy to cow milk, egg, peanut and fish, However not every child with atlergic reactions will have positive skin or blood tests. The most important test is a challange with the problem food. In this test, foods suspected of causing an allergic reaction are carefully given to the child under the watchful eye of specially trained staff.
Some children also require special tests of bowel function to assist in diagnosis.
There are no standardizations of dosage and time intervals between challenges. Skin tests and blood tests are both used in the diagnosis of IgE-mediated reactions to allergens. A positive skin test is dependent not only on IgE antibody but also on mast cell integrity and vascular and neural responsiveness. However, skin tests are not quantitative, and the results cannot be compared between clinics. In contrast to in vitro tests, skin tests are dependent on the skin status, and are influenced by medication and the way the test is performed.