If a food allergy is suspected, your doctor will take a detailed history of your eating and dietary habits, as well as past reactions you’ve had to foods similar to the one that is being proposed as an allergen.

Food Diary and Elimination Diet

To identify the culprit, your doctor may ask you to keep a food diary describing your eating selections, symptoms that arise, and any medications you may be taking. In addition, you may be advised to eliminate the suspected foods from your diet for a couple of weeks and subsequently add them back one at a time. If you’ve had severe reactions to foods, this technique will not be safe to use for diagnostic efforts.

Skin-Prick Test

Specific antibodies to the suspected foods will likely be demonstrated by blood or skin tests, especially the latter in which a bit of each problem food is inserted under the skin. If the skin develops a bump or other noticeable change of appearance, you are allergic to that food.

RAST Test

Your doctor may want to do a blood test rather than a skin test. A RAST test (short for “radioallergosorbent test”) can measure your immune system’s response to an allergen by detecting the amount of IgE antibodies made in response to suspected food proteins. In a RAST test, a sample of the patient’s blood is added to the suspected food protein, and then tested for the amount of IgE antibodies made in response.

 

Conditions That Resemble a Food Allergy

Correct diagnosis of a food allergy may be made more difficult given the number of fairly common conditions that can trigger similar symptoms.These include:

Food intolerance

Some people lack specific enzymes that are needed to digest particular foods. Lactose intolerance, which can cause bloating, cramping, and other abdominal symptoms that mimic a food allergy reaction, is perhaps the best known. Dairy products, which are a major source of lactose, may need to be avoided.

Food poisoning

Toxins in foods such as mushrooms, rhubarb, spoiled tuna, and other fish may trigger serious reactions. Other causes of food-borne illness include raw egg, undercooked meat, spoiled cheese, processed meats, and unwashed produce.

Food additive sensitivity

Sulfites and other food preservatives, monosodium glutamate, artificial sweeteners, and food coloring agents can all spark adverse physical reactions.

Celiac disease

This chronic digestive disorder is often referred to as a gluten allergy, but it is not a true allergy even though it does involve an immune system response. This complex reaction to gluten—which is found in wheat and other grains used primarily in baking—attacks the lining of the small intestine, preventing the absorption of several nutrients. In its worst cases, Celiac disease may lead to malnutrition, while milder forms of the condition result in cramping, bloating, and abdominal pain.

Irritable bowel syndrome (IBS)

IBS can cause significant abdominal symptoms, including severe constipation, bloating or diarrhea. Trying to avoid the foods that trigger this condition is critical to avoiding the symptoms.