Food Allergy Diagnosis

Written by the Healthline Editorial Team | Published on July 21, 2014
Medically Reviewed by George Krucik, MD, MBA on July 21, 2014

Diagnosing Food Allergies

Diagnosing a food allergy is sometimes difficult and may involve a number of tests. This is because food allergy symptoms may resemble those of a number of other conditions.

Symptoms may center on a particular body area, such as the gastrointestinal system, so doctors have to rule out other conditions that can cause similar symptoms.

Diagnostic Methods for Food Allergies

Medical History

If a food allergy is suspected, your doctor will start by asking you to provide a detailed history of your eating and dietary habits. They will also ask questions about any past reactions you’ve had to certain foods.

According to the National Institute of Allergy and Infectious Diseases (NIAID), your doctor may also ask any of the following questions:

  • Did your reaction come on quickly, usually within several minutes after eating the food?
  • Is your reaction always associated with a certain food?
  • How much of this potentially allergenic food did you eat before you had a reaction?
  • Have you eaten this food before and had a reaction?
  • Did anyone else who ate the same food get sick?
  • Did you take allergy medicines, and if so, did they help? (For example, antihistamines should relieve hives)

Your doctor may also wish to perform a physical exam to rule out other suspected medical conditions.

Food Diary and Elimination Diet

To identify the culprit, your doctor may ask you to keep a food diary to record your eating selections, symptoms, and any medications you may be taking.

They might then advise you to avoid suspected foods for a couple of weeks and gradually add them back one at a time. If your symptoms and reactions are severe, this technique might not be safe.

Skin-Prick Test

A skin-prick test is one of the primary tests used to diagnose a food allergy. For this test, a tiny bit of each potentially problematic allergen (food protein) is inserted under the skin. If the skin develops a bump or other noticeable change of appearance, you are likely to be allergic to that particular protein. Results can usually be seen in 15 to 30 minutes.

Some individuals test positive in the skin-prick test for a certain food allergy without actually having this allergy. Doctors will consider test results in conjunction with your symptoms history in order to make a more conclusive diagnosis.

RAST Test

Your doctor may want to order a blood test rather than a skin test, or they may order both.

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 blood is added to the suspected food protein and then tested for the amount of antibodies made in response.

As with the skin-prick test, a positive result does not always mean an individual has the particular food allergy. Results will be considered along with the patient’s history of reactions to the particular food to make a more accurate diagnosis.  

Oral Food Challenge

For this test, your doctor will provide you with small amounts of the foods that are suspected allergens. He or she will steadily increase the amount of the suspected foods while monitoring your reaction to each one.

For this task, you may be asked to wear a mask to make your diagnosis more accurate. Some people may have a bodily reaction simply by seeing a particular food or even thinking about it. Sometimes, the allergist will not know (during the test) which foods he or she is giving you as well.

This test may also be used to determine whether an individual has a diminished response to an allergen.  

Conditions That Resemble a Food Allergy

Correct diagnosis of a food allergy can be difficult because several fairly common conditions can trigger similar symptoms.

Food Intolerance

Some people lack specific enzymes required to digest certain foods. One common food intolerance is lactose intolerance, which can cause bloating, cramping, and other abdominal symptoms that mimic a food allergy reaction. With this condition, dairy products (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 similar to those of a food allergy. 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 (MSG), artificial sweeteners, and food-coloring agents may spark adverse physical reactions.

Celiac Disease

Celiac disease is a chronic digestive disorder. It is sometimes 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. Milder forms of the condition result in cramping, bloating, and abdominal pain.

Irritable Bowel Syndrome (IBS)

IBS is a digestive disorder that can cause significant abdominal symptoms, including severe constipation, bloating, or diarrhea. Doing your best to avoid the foods that trigger this condition is critical to avoiding symptoms.

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