If you think you might have either a food allergy or intolerance, speak to your GP or a dietitian first. If you take a test without proper medical advice, you could be wasting your money. Below is a guide to the main tests that are available. Only a few are known to be effective at identifying food allergies.
Skin prick testing (SPT)
Drops of diluted foods suspected of causing allergy are placed onto your arm or back. Then the skin is pierced, through the drop, using a small needle. Itching, redness and swelling indicate a positive reaction.
Tests for: food allergy.
Pros: cost-effective. Safe for all ages. Negative results are 95% accurate.
Cons: a positive SPT is only around 55% accurate because often a patient will test positive to a food that does not cause a problem.
Further information: available on the NHS, although there may be a waiting list.
IgE blood tests
These measure levels of IgE antibodies to specific foods in the blood.
Tests for: food allergy.
Pros: negative results are fairly reliable (around 90%).
Cons: false negatives are possible, especially if you have stopped eating the food already. Positive tests are about 55% accurate.
Further information: available on the NHS, although there may be a waiting list. Some private laboratories offer IgE blood tests that you pay for.
Food challenge testing
This tests your response to consuming a small amount of a food thought to cause allergy.
Tests for: food allergy and any other acute sensitivity.
Pros: double blind challenging is considered the most reliable test. This is where neither you nor the tester knows which food sample is being given.
Cons: time consuming, costly and sometimes risky. It cannot be performed on people with asthma or those at risk of a severe allergic reaction.
Further information: available on the NHS.
Hydrogen breath test
In this test, a patient is given a mixture of milk and water. The breath is then tested to measure for hydrogen levels and a rise suggests a lactose intolerance.
Tests for: lactose intolerance and other, rarer, sugar intolerances.
Pros: good accuracy.
Cons: time consuming. False positive and false negative results are possible.
Further information: available on the NHS and in some private clinics.
Commercial coeliac test
These are tests you can do yourself at home, by pricking your finger to test a small drop of blood. They provide a result in 10 minutes.
Tests for: coeliac disease only.
Pros: they are around 95% accurate.
Cons: there is a 5% chance that undiagnosed coeliac disease sufferers will test negative. Patients testing positive may require a biopsy of the intestine to confirm the diagnosis. A blood test is available through your doctor.
Dietary exclusion and reintroduction
Conducted by a dietitian, foods that may be causing you a problem are removed from your diet until symptoms disappear. Then each food is individually reintroduced and reactions recorded.
Tests for: food intolerance.
Pros: the re-introduction of a food followed by the return of symptoms strongly suggests an intolerance to that food.
Cons: high motivation required to stick to the strict diet and routine.
Further information: most people will be able to see a registered dietitian within the NHS after being referred by a GP. You can also self-refer. Consultations with dietitians within the NHS are free.
To find a dietitian privately, try the Dietitians Unlimited website. To check that your dietitian is registered, visit the Health Professions Council website.
Commercial blood tests
A small blood sample is submitted to a private laboratory for analysis of IgG antibodies.
Tests for: food intolerance.
Pros: supported by Allergy UK.
Cons: expensive (£250). Limited evidence that they work. May leave patients on an inadequate diet.
Kinesiology tests
This claims to find imbalances in the body by testing the strength of your muscles. If food intolerance is suspected, the patient’s skin will be exposed to different foods for signs of weakness in the muscles.
Tests for: all food intolerances, including psychological ones.
Pros: no needles or blood samples are needed.
Cons: only available privately (at a rate of about £40-£60 an hour). Regarded by mainstream allergists as unreliable and unscientific.
Vega testing
A programme of elimination and re-introduction of foods partly based on the patient’s diet and on the results of Vega testing. In this test, changes in the skin’s resistance in response to exposure to different foods are monitored within an electrical circuit.
Tests for: food intolerances, except those to peanut and gluten.
Pros: widely available. Non invasive.
Cons: no evidence of effectiveness in diagnosing food intolerances.
Commercial antibody test
Food extracts are combined with blood samples and then examined. Changes to size, shape and quantity of white blood cells are said to suggest a problem food.
Tests for: food and chemical sensitivities not caused by antibodies.
Pros: several modest trials show the technique may be worthy of closer investigation.
Cons: no study has ever shown the test to be accurate.
