When you suspect that you or a loved one has a food allergy, you’ll want to get an official diagnosis. More and more, patients are seeing offerings and advertisements for IgG test kits that claim to identify food allergies and sensitivities. But what are they? And, is that the correct test for diagnosing a food allergy?
What is an IgG test?
IgG tests – known as food sensitivity tests – measure your immune-antibody response to foods. Specifically, it measures something in your immune system called immunoglobulin G – the body’s most abundant antibody that protects against bacterial and viral infections. These kits require a blood sample (sometimes through a fingertip) that gets mailed back to a laboratory to evaluate. Kits test against around 100 food products and food additives, sending you back results and recommendations.
How does IgG fit in with food allergies?
According to Dr. Dave Stukus of Nationwide Children’s Hospital, IgG cells are more of a memory antibody – they don’t predict food allergy or food intolerance. Instead, IgG cells are a response of the immune system after the body has been exposed to a food. It’s no wonder some people get results many items long – it indicates they have a varied diet, but does not suggest food allergy nor food intolerance.
According to the American Academy for Allergy, Asthma and Immunology (AAAAI): “IgG and IgG subclass antibody tests for food allergy do not have clinical relevance, are not validated, lack sufficient quality control, and should not be performed.”
The European Academy of Allergy and Clinical Immunology says the presence of IgG4 antibodies “should not be considered as a factor which induces hypersensitivity, but rather as an indicator for immunological tolerance… In conclusion, food-specific IgG4 does not indicate (imminent) food allergy or intolerance, but rather a physiological response of the immune system after exposition to food components. Therefore, testing of IgG4 to foods is considered as irrelevant for the laboratory work-up of food allergy or intolerance and should not be performed in case of food-related complaints.“
In other words, they don’t recommend it as a diagnostic tool for food allergy or intolerance because it may result in unnecessarily avoiding healthy foods and cause undue stress and anxiety.
What is an IgE test and how does it differ from IgG?
Not to be confused with IgG tests, IgE tests are associated with food allergy and allergic responses. An IgE test measures immunoglobulin E, the antibody responsible for initiating and perpetuating an allergic reaction. It is measured through a blood test and the results are given as a number to indicate your likelihood of being allergic.
Are there other diagnostic tests?
Yes. Skin prick test are also often used. The skin is lightly irritated with a liquid form of various allergens. If allergic, the skin will develop a hive at each allergic location. The size of that hive will remeasured and recorded.
The gold standard of testing for food allergy remains the oral food challenge. Under medical supervision, a patient is given small, then increasingly bigger amounts of an allergen, and monitored for signs of reaction. If they show no signs, it means their body tolerates that food and they are usually not considered allergic. If they react, it means their body does not tolerate the food, they are considered allergic and that food should be avoided. [To learn more about Oral Challenges, read What is an Oral Food Challenge and How to Prepare]
If you suspect you or someone you know has a food allergy, be sure to talk to a doctor and get the right test so that you can make healthy decisions about how to stay safe and feel great.