Diagnosing food allergy  

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

Your GP 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 types of symptoms have been experienced, and if not, how often have they occurred?
  • What food was involved and how much of it did your child eat?

They will also want to know about your child’s medical history, such as:

  • Does your child 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 are growing at the expected rate.

Referral to an allergy clinic

If your GP thinks that you or your child has 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 your child had symptoms that came on quickly (an IgE-mediated food allergy) you will probably be given a skin-prick test or a blood test.
  • If your child’s symptoms developed more slowly (non-IgE-mediated food allergy) you will 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 skin cells. 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, so testing should only be carried out where there are facilities that can deal with an anaphylactic reaction. This would usually be at an allergy clinic or centre, a hospital or a 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In a food elimination diet, the food that is thought to have caused the allergic reaction is withdrawn from your or your child’s diet for two to six weeks. The food is then reintroduced into the diet. 

If the symptoms go away when the food is withdrawn, but return once the food is introduced again, this normally means your child has 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 your child needs any alternative sources of nutrition.
  • How long the diet should last.

Do not 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. They include:

  • Vega testing, which claims to detect allergies by measuring changes in your electromagnetic field.
  • Kinesiology testing, which claims to detect food allergies by studying your muscle responses.
  • Hair analysis, which 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), which 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 alleged to be based on are unproven and independent reviews have found them to be unreliable. Therefore, they should be avoided.

Picture of skin prick testing

A skin prick test is usually the first test recommended by a doctor for a suspected allergy 

Questions to ask

If your child is diagnosed with a food allergy (or you are 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 child’s health (or your own 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: 25/04/2014

Next review due: 25/04/2016