The truth about allergy testingBlood tests (IgG)

YorkTest Laboratories and Cambridge Nutritional Sciences Ltd (CNS) are the main companies that advertise these blood tests. They cost between £99 and £275, depending on how many foods your blood is tested against. 

A pinprick blood test can be unreliable

They use a sample of blood and test it against a range of foods to detect levels of an IgG (immunoglobulin G) antibody. They claim that raised levels of IgG antibodies within your blood indicate food intolerance. 

What we did 

The company sends you a small surgical pin to prick yourself with, and a vial to collect the blood sample. You post back the sample to be tested. Our researcher Clare said: ‘I found the CNS test hard to do and had to prick myself several times to get the right amount.’ 

Researcher Adam sent one blood sample to YorkTest for the IgG blood test and one to CNS taken on the same day. A few days later, so as not to arouse suspicion, he sent a duplicate sample to YorkTest under a different name. Clare did the same, but sent her duplicate sample to CNS. Results are provided in a table telling you the level of reaction to each food. 

Our findings

Adam has a severe peanut allergy, yet only one of the results showed any possible sensitivity to peanuts. Of 56 foods identified as problematic for Clare, who has no known allergies or intolerances nor any symptoms, only 21 matched on results from both companies. 

There were even differences between the original and duplicate blood test results from the same companies. Only 34 of 42 foods appeared on both results from CNS for Clare, with varying levels of reaction. 

Experts’ verdict

Although IgG testing is a validated scientific test, our three experts believe that, in line with our findings and other published research, its use in diagnosing food intolerance is difficult to prove scientifically. IgG antibodies are commonly found in healthy people and do not prove intolerance, only that the food itself has been eaten. 

The experts were also concerned that the diets recommended by these tests exclude up to 39 foods – which could lead to nutritional problems. Analysis of blood samples produced differing results.