Diagnosing Food Allergy

The doctor will first take a careful history to determine what the offending food might be and whether the time between eating the food and the onset of symptoms suggests an allergic response. Possible investigations include skin prick tests, in which dilute solutions are made from foodstuffs. A drop of each solution is put on the skin, which is pricked with a needle; the skin is then monitored for a reaction. These tests are not always reliable because a significant number of people who test positive to a certain food will not have allergic symptoms when they eat it. However, negative results are more reliable and virtually rule out the possibility of allergy to the food tested.

In some cases of suspected food allergy, blood samples are taken and antibody levels to certain food proteins measured. Known as RAST tests, these investigations are less reliable than skin tests.

If a skin test or a RAST test for a particular food is positive and the diagnosis is backed up by the symptoms described, the food should be tested using a double-blind food challenge. In this test, responses are monitored to the food and to a placebo. These are presented in such a way that neither the patient nor the investigator knows which is which. Read the rest of this entry »