Food allergy - Diagnosis 

Diagnosing food allergy  

Picture of skin prick testing

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

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

It is likely that 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?
  • Was this the first time your child has had these types of symptoms, and if not, how often have symptoms occurred?
  • What food was involved and how much of the food 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 your family?
  • Was (or is) your child breastfed or bottle-fed?

Your GP may also asses your child’s weight and size to make sure that they are growing at the expected rate.

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

If your child had symptoms that came on quickly (an IgE-mediated food allergy) then it is likely that they will be given what is known as a skin-prick test. The doctor may also want to give them a blood test.

If your child’s symptoms developed more slowly (non-IgE-mediated food) then it is likely that they will be put on what is known as a food elimination diet.

More information on these types of test is given below.

Skin-prick testing

During a skin-prick test, drops of diluted foods are placed on the arm. The skin is then pierced, through the drop, using a small needle or pin to introduce the food drops to the system. Itching, redness and swelling would usually indicate a positive reaction. This is usually painless.

A skin-prick test does have a small chance of causing anaphylaxis, so testing should only be carried out where there are facilities available to deal with an anaphylactic reaction. This would usually be at an allergy clinic or centre, hospital or a larger GP surgery.

Blood test

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

Food elimination diet

In a food elimination diet, the food suspected of causing the allergic reaction is withdrawn from your or your child’s diet for two to six weeks.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 your child’s symptoms go away when the food is withdrawn and then return once the food is introduced then this can normally confirm your child has a food allergy.

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

  • the food and drinks you need to avoid
  • how you should interpret food labels
  • whether 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 which claim to detect allergies. They include:

  • Vega testing, which claims to be able to detect allergies by measuring changes in your electromagnetic field.
  • Kinesiology testing, which claims to be able to detect food allergies by studying your muscle responses.
  • Hair analysis, which claims to be able 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 tests have been found to be unreliable. They should therefore be avoided.


Page last reviewed: 10/01/2012

Next review due: 10/01/2014

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Comments

The 1 comments posted are personal views. Any information they give has not been checked and may not be accurate.

Julie D L Smith said on 29 March 2013

It would be really helpful to have some clinical evidence to support some of these alternative tests as they have helped many people in our experience. Whilst this may be based on anecdotal evidence this does appear to have a place in supporting many people who have a range of symptoms from IBS to stomach bloating/discomfort and weight gain. There would be a huge support from many members of the public and practitioners who have either received these alternative therapies or who practice them to research and provide evidence so that some of these may be accepted by the NHS. Anecdotal evidence should be taken seriously as it is based on first hand experience of those who have actually tried these tests and have experienced an improvement in their symptoms. It is not fair for the medical profession to continually ridicule the work of many alternative health practitioners who have studied and been in practice for many years and have had extremely good results. It should be remembered that everyone has a choice where to go for healthcare and those individuals who choose alternative healthcare would not do this if they found it ineffective. Alternative therapies are not offered as part of the NHS and therefore have to be paid for by those who wish to seek an alternative method of helthcare. It stands to reason that they would only do this if they were obtaining positive results in the maintainence and improvement of their symptoms. I think there should be more respect for alternative therapies, practitioners and members of the public who choose this route to their own healthcare.

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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), questions you may wish to ask may include:

  • What type of allergy is suspected?
  • What is the risk of 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?

Allergy testing

If you think you have an allergy, here's advice on how to get diagnosed with NHS-approved allergy tests