How Are Food Allergies Diagnosed?

Reviewed by: HU Medical Review Board | Last Reviewed: March 2022

Diagnosing a food allergy can be challenging. The person may not have the same allergic reaction every time, and symptoms can vary between different people.1

It is important to see a doctor and be tested if you suspect a food allergy. Many times, people self-diagnose themselves with a food allergy when they really have a food sensitivity or intolerance. It is important to have an accurate diagnosis because the treatment and risks are different for allergies and intolerances.1

To diagnose a food allergy, you will need to see a specialist. An allergist will conduct a physical exam and ask about all possible allergy symptoms and other health conditions. Then, there might be a series of tests. It may take several weeks to get answers if you need to follow a special diet or do a food challenge test to confirm your diagnosis.1

Physical exam and medical history

A physical exam includes weighing you and checking your blood pressure. The doctor will also check the other organ systems in your body. This includes looking in your eyes and ears, tapping on certain areas, and listening to your heart and breathing.1

This gives the doctor basic information about your overall health. After the physical exam, your doctor will take your medical history.

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An accurate, detailed description of symptoms

Be ready to describe your medical history in detail and as accurately as possible. Come with a list of the medicines and supplements you take, and any surgeries and illnesses you have had. This helps your doctor get all the information needed to diagnose and treat your food allergy. This may not be easy, but taking notes ahead of time can help you remember.
Questions your doctor may ask you include:1

  • What were you eating when you first noticed these symptoms?
  • How quickly did symptoms appear?
  • Has this reaction happened before?
  • What symptoms did you develop?
  • How long did the symptoms last?
  • Did you try to treat it with any medicine?
  • Do the symptoms occur with any other foods?
  • Was there something else that may have triggered your symptoms?
  • Have you ever eaten the food before or since and not had a reaction?
  • Do your symptoms get in the way of school, work, or socializing?
  • Does anyone else in your family have allergies? If yes, what kind?
  • Do you use any prescription, over-the-counter, or recreational drugs?

You may also be asked about your work, hobbies, and exercise habits. Next, your allergist may recommend an elimination diet, skin test, blood test, or a food challenge test.1

Elimination diet

An elimination diet is a special diet used to narrow the list of foods you may be allergic to. You will keep a diary and record all the foods, drinks, and medicines you take each day and when. You will then list all your symptoms and what time those began.1

If 1 or 2 foods seems to cause an allergic reaction, you will be asked to avoid those foods for 1 to 2 weeks. Your doctor will look to see if your symptoms go away while not eating those foods and then flare up when you eat the food again. More tests will be needed to decide if you have a food allergy or food intolerance.1

Blood and skin tests

Skin and blood tests may be used to help rule a food allergy in or out. However, these tests will not tell you or your doctor how severe your reaction to a food may be. And, these tests are not always conclusive. Some people test positive for a food allergy and yet have no symptoms when eating that food.1

Skin prick tests take place in a doctor’s office. A nurse or allergist will place a drop of food extract onto your skin and scratch it in. Then, you wait for about 15 to 30 minutes for results. Your test is considered positive if a wheal develops at that site. A wheal looks like a mosquito bite bump. The size of the wheal does not predict how severe your allergic reaction to a food will be.1

Blood tests are less sensitive than skin prick tests. However, your doctor may wish to find out how many IgE antibodies you have in your blood. This is the test ordered if you cannot do a skin test because you are on drugs that affect the result or if you have certain skin conditions.1

Sometimes, blood tests are done alongside skin tests to help with the diagnosis. Results usually take 1 to 2 weeks. Like skin prick tests, these results do not tell your doctor how severe your allergic reaction to a food might be.1

Food challenge test

Your doctor may order a food challenge test to confirm your food allergy, if the diagnosis is unclear. This is the gold standard for diagnosing a food allergy. However, this test can be time-consuming, expensive, and in some cases, dangerous. For these reasons, your doctor may not order a food challenge test.1

For this test, you will be given the suspected food allergen in gradually larger doses. The food is given under close supervision. Then you will be observed for any reactions. Emergency equipment and epinephrine must be close by during the test due to the risk of anaphylaxis.1

A food challenge may also tell your doctor if you have outgrown a food allergy.1