Diagnosing food allergy  

If you think you or your child has a food allergy, make an appointment with your GP.

They will ask you some questions about the pattern of your child's symptoms, such as:

  • How long did it take for the symptoms to start after exposure to the food?
  • How long did the symptoms last?
  • How severe were the symptoms?
  • Is this the first time these symptoms have occurred? If not, how often have they occurred?
  • What food was involved and how much of it did your child eat?

They'll also want to know about your child's medical history, such as:

  • Do they have any other allergies or allergic conditions?
  • Is there a history of allergies in the family?
  • Was (or is) your child breastfed or bottle-fed?

Your GP may also assess your child's weight and size to make sure they're growing at the expected rate.

Referral to an allergy clinic

If your GP suspects a food allergy, you may be referred to an allergy clinic or centre for testing.

The tests needed can vary, depending on the type of allergy:

  • if the symptoms developed quickly (an IgE-mediated food allergy) – you'll probably be given a skin-prick test or a blood test
  • if the symptoms developed more slowly (non-IgE-mediated food allergy) – you'll probably be put on a food elimination diet

There is more information on these tests below.

Skin-prick testing

During a skin-prick test, drops of standardised extracts of foods are placed on the arm. The skin is then pierced with a small lancet, which allows the allergen to come into contact with the cells of your immune system.

Occasionally, your doctor may perform the test using a sample of the food thought to cause a reaction.

Itching, redness and swelling usually indicates a positive reaction. This test is usually painless.

A skin-prick test does have a small theoretical chance of causing anaphylaxis, but testing will be carried out where there are facilities to deal with this – usually an allergy clinic, hospital, or larger GP surgery.

Blood test

An alternative to a skin-prick test is a blood test, which measures the amount of allergic antibodies in the blood.

Food elimination diet

In a food elimination diet, the food thought to have caused the allergic reaction is withdrawn from the diet for two to six weeks. The food is then reintroduced.

If the symptoms go away when the food is withdrawn but return once the food is introduced again, this normally suggests a food allergy or intolerance.

Before starting the diet, you should be given advice from a dietitian on issues such as:

  • the food and drinks you need to avoid
  • how you should interpret food labels
  • if any alternative sources of nutrition are needed
  • how long the diet should last

Don't attempt a food elimination diet by yourself without discussing it with a qualified health professional.

Alternative tests

There are several shop-bought tests available that claim to detect allergies, but should be avoided.

They include:

  • vega testing – claims to detect allergies by measuring changes in your electromagnetic field
  • kinesiology testing – claims to detect food allergies by studying your muscle responses
  • hair analysis – claims to detect food allergies by taking a sample of your hair and running a series of tests on it
  • alternative blood tests (leukocytotoxic tests) – claim to detect food allergies by checking for the "swelling of white blood cells"

Many alternative testing kits are expensive, the scientific principles they are allegedly based on are unproven, and independent reviews have found them to be unreliable. They should therefore be avoided.

Questions to ask

If your child is diagnosed with a food allergy, or you're an adult who has just been diagnosed with a food allergy, you may want to ask questions such as:

  • What type of allergy is it?
  • What are the chances of having a severe allergic reaction?
  • Will the allergy have an impact on other areas of my or my child's health, such as diet, nutrition and vaccination? Some vaccines contain traces of egg protein.
  • Is my child likely to grow out of their allergy and, if so, when?

Page last reviewed: 16/05/2016

Next review due: 01/05/2019