Tests for allergies and intolerances

The best ways to find out if your baby has a food allergy or intolerance - plus a few that are a waste of money.

Wondering if your baby has an allergy or intolerance can be a stressful time. As well as dealing with the unpleasant symptoms, you also have an anxious wait while you're referred to a specialist GP or allergist. During this time, you may be struggling to avoid certain foods in order to keep your child’s symptoms from getting worse.
You might have heard that there are places on the high street which can test for allergies in one day. But are they worth using, and should you trust the results?

Many of these high street tests are based on complementary and alternative medicine and aren't supported by any scientific evidence, unlike the tests your GP will prescribe, which have been proven to be safe and effective.

The high street tests may sound tempting, but they can cost quite a lot of money, and many of them recommend avoiding lots of different foods or taking herbal supplements. In the long term, avoiding lots of foods without any proof of an allergy could mean your little one isn't getting the right nutrition to grow up healthy.

Tests which your doctor may request:

  • Skin prick test (SPT) – During this test, an allergist will place drops of solutions containing different potential allergens on the skin, then use a tiny lancet to prick through the solution and into the top layers of the skin. A few minutes later, the allergist will check to see whether the skin has reacted by swelling or turning red; this shows a specific type of allergy called an ‘IgE allergy’.
  • Blood tests (RAST or ‘specific IgE’ test) – This involves taking a blood sample and counting the number of ‘IgE’ antibodies it produces in response to the suspect food.
  • Food challenge – In this test, the allergist will place very small amounts of the suspect food in your baby's mouth and observe any symptoms (under medical supervision).
  • Food exclusion and reintroduction – This 'test' involves removing the suspect food from your baby's diet to see what effect this has on symptoms. If the symptoms improve, then your doctor may suggest re-introducing the food briefly to see if the symptoms return.

High street tests available:

  • ‘IgG’ blood test – This test is meant to measure the amount of ‘IgG’ (an antibody which sounds similar to the ‘IgE’ antibody involved in true allergies, but which is completely different) the blood produces when exposed to a suspect food. While it sounds a lot like the RAST/IgE tests mentioned above, this test is completely different. Levels of ‘IgG’ do not reflect an allergy, and they could even mask one.
  • Kinesiology (muscle testing) – This is based on a theory that certain foods can disrupt energy fields and cause muscle weakness. There is no scientific evidence to support this theory, and this test could result in many different foods showing ‘positive’ for an allergy.
  • Hair analysis – Testing a lock of hair in a laboratory to show heavy metal levels or nutrient deficiencies. Whilst these tests may well check these levels, they have no relation to whether someone has an allergy or not.
  • Leucocytotoxic test – This sounds scientific: a blood sample is taken, and the white blood cells are mixed with the allergen. If the white blood cells swell, practitioners say this indicates an allergy. However, there is no scientific evidence to suggest that this test is at all accurate.
  • VEGA/Electrodermal test – This is based on a theory that electromagnetic currents in the body change when presented with a food that the patient is allergic to. However, there is no scientific evidence to support this test.
  • Others – Other analysis which might be offered include blood analysis ‘while you wait’, stool sample analysis and tests on urine and saliva.

Of course, the decision you make about allergy testing is entirely up to you; however, going through your GP ensures you will only be seen by trained professionals, using techniques which have been thoroughly studied and have good quality evidence to show that they work.

If you would rather get NHS-approved allergy testing done privately, Allergy UK has a list of accredited specialists who can help.