Recently, I have noticed a rise in the promotion of food allergy blood tests (called IgG Food Allergy Tests), claiming to help patients identify exactly which foods they are allergic to, so that they can definitively know which foods to remove from their diet.

This article seeks to clarify some misconceptions that you may have about such tests.

What is a food allergy?

A food allergy is when a person’s immune system responds as if a certain food is harmful to the body. If a person eats or touches that food, they can have an allergic reaction. In some cases, breathing in tiny pieces of the food can also cause a reaction. Most allergic reactions happen within 5 minutes to 1 hour after eating or touching the food.

What are the symptoms of food allergy?

Mild symptoms can include itchy skin (hives), itchy eyes, swelling of eyes, runny nose or sneezing.

Severe symptoms are also called “anaphylaxis.” They can include swelling of the throat, wheezing, difficulty breathing, vomiting, diarrhoea, giddiness, fainting and even death.

What are the differences between food allergy and food intolerance/sensitivity?

Food intolerance or food sensitivity are more common than food allergies and are not caused by the immune system.

For such reactions, the body may just not be digesting the food properly and this is not usually dangerous, although these reactions can cause unpleasant symptoms.

Examples include lactose intolerance, heartburn, food poisoning, and sensitivity to caffeine.

How do you diagnose food allergy?

Diagnosis of food allergy requires a thorough history with careful evaluation of the symptoms and how they relate to the food consumed.

After that, the doctor can order tests or make a referral to an allergy specialist if a food allergy is suspected based on the history.

What are the tests for food allergy?

Skin test – Most skin tests involve pricking the skin with a device that contains a tiny amount of a food. If there is a resulting red, itchy bump, it means that you are allergic to that food. Some devices can test for several different food allergies at once.

Blood test – Blood tests for food allergies look for antibodies (proteins) called “IgEs” that the body makes when it is having an allergic response. Such tests are generally only available at the allergy specialist clinic.

Note: Tests for specific foods should only be ordered based on the symptoms rather than as a whole panel of tests including foods that do not cause any symptoms at all. These tests by themselves are not able to diagnose food allergies without correlation to the history of symptoms.

What about IgG blood test?

IgG is another type of antibody that the body produce. Current research shows that the presence of specific IgG to food is a marker of previous exposure to the food, not a marker of allergy to the food.

This means that a high IgG level to a food does not indicate allergy to that food, whereas a low IgG level to a food does not mean no allergy to that food. This essentially makes the test useless in the diagnosis of food allergy, especially more so if offered as a whole panel without correlating to the symptoms.

What are the harms of doing the IgG blood test anyway?

Other than being costly with no diagnostic usefulness, the main harms come in when patients actually make dietary changes based on this blood test results.

False diagnosis of food allergy based on IgG test can lead to unnecessary and impractical dietary restrictions, as well as decreased quality of life.

What is of greater concern is that a patient with a true food allergy may be falsely assured by an unelevated IgG level to that particular food and hence start taking that particular food, which can cause potentially deadly allergic reactions.

Take Home Points:

• Do not go for IgG food allergy tests.
• If you suspect that you could be having a food allergy, speak to your doctor first. It will be useful to keep a food and symptoms diary to discuss with your doctor.
• Skin prick or IgE tests should only be ordered by the doctor for specific food items for which allergies are suspected, based on your history, rather than as a whole panel.

Useful Materials:

• American Academy of Allergy, Asthma & Immunology: https://www.aaaai.org/tools-for-the-public/conditions-library/allergies/igg-food-test

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