What should you do if you suspect you have a food allergy?

The Food Allergy Network's Anne Munoz-Furlong suggests keeping a food diary as a first step, writing down everything you eat or drink for a one- or two-week period. Note any symptoms and how long it took for such symptoms to develop.

But Furlong and other experts agree that those who suspect food allergies also need to be evaluated by a physician with intensive specialty training in allergy and immunology. Be sure to discuss what diagnostic and treatment plan is anticipated, and the costs.

Ask if the tests have been proven effective by accepted standards of scientific evaluation.

"Go to a board-certified physician who is an allergy expert," advises Paul C. Turkeltaub, M.D., associate director of the division of allergenic products and parasitology at FDA's Center for Biologics Evaluation and Research. "Be very wary of claims of food allergy to explain chronic, common complaints."

The diagnosis of food allergy requires a careful history, physical exam, appropriate exclusion diet, and diagnostic test to rule out other conditions. Tests can include direct allergy skin tests, blood tests, or "elimination and challenge" tests for suspected foods.

The most accurate kind of test is a controlled challenge test, often done in "blind" or "double-blind" fashion to eliminate psychological factors. In a blind challenge, the patient is given either a sample of the food, without being told what it is, or a placebo, an inert substance used as a control in the test. The observer (a doctor or assistant), however, knows what the substance is. Both patient and observer record any symptoms of allergic reaction. In a double-blind challenge, neither the patient nor the observer knows if the patient is given the food (allergen) or the placebo.

In recent years, unproven tests such as "food cytotoxic blood tests" and "sublingual provocation food testing" have been promoted as supposed "diagnostic" tools to detect food allergies. FDA believes that food cytotoxic blood tests are not supported by well-controlled studies and clinical trials.

In food cytotoxic testing, a test tube of blood is taken from the patient. The white cells (leukocytes) are mixed with plasma and sterile water and placed on microscope slides coated with dried extracts of a particular food. The reaction of the cells is then examined under a microscope; if they change shape, disintegrate, or collapse--or the person examining them says they do--the patient is supposedly allergic to that particular food. Test results may be interpreted by a "nutritional counselor" working on commission, who recommends vitamins and minerals (often available on site) that the patient needs to correct his or her "allergic condition." But FDA and other experts emphasize there is no evidence that such tests are valid in diagnosing food allergies.

Sublingual provocation food testing dates back to 1944. The test consists of placing three drops of an allergenic extract under a patient's tongue and waiting 10 minutes for any symptoms to appear. When the doctor is satisfied he has determined the cause of the symptoms, he administers a "neutralizing" dose, which is usually three drops of a diluted solution of the same allergenic extract. The symptoms are then expected to disappear in the same sequence in which they appeared. Advocates claim that if the neutralizing dose is given before a challenge test (for instance, eating a meal containing the offending food), the person will not have symptoms.

But after careful study of existing data, The American Academy of Allergy and Immunology says no controlled clinical studies demonstrate either diagnostic or therapeutic effects of sublingual provocation food testing. The academy concludes that use of the tests should be reserved for experiments in well-designed trials.

If you are diagnosed with a food allergy, scrutinize food labels to detect potential sources food allergens. When eating out, ask about ingredients if you are unsure about a particular food; ask to talk to the manager of the restaurant about ingredients in specific dishes.

Keeps epinephrine with you and know how to administer it. If you do experience a reaction, seek medical attention immediately, even if the symptoms are mild or seem to subside. Mild symptoms may be followed 10 to 60 minutes later by the onset of severe problems.