Explanation

Food allergen screen (fx5): what is measured?

The test measures, in one go, IgE antibodies against a fixed mix of 6 foods: chicken egg white, cow's milk, cod, wheat, peanut and soy. Fx5 is the code of the mix; the number 5 does not stand for the number of allergens. IgE is the type of antibody that, in an allergic reaction, triggers mast cells to release histamine; the body only makes these antibodies after it has previously been in contact with the allergen, and this is called sensitization. Because the 6 allergens are tested together, the result gives one number and a verdict of positive or negative, but not which food the antibodies are directed against.

What can it detect?

Sensitization to at least one of the 6 foods in the mix: the body has made IgE antibodies against one or more of them
A first indication of whether an acute reaction shortly after eating may be related to one of these foods

Result

What does the result mean?

Positive result

A positive result means that you have IgE antibodies against at least one of the foods in the mix: sensitization. That is not the same as an allergy, and the test does not say which food the antibodies are directed against. A positive result only counts if there has also been a clear reaction shortly after eating: itching in the mouth, hives, swelling, abdominal symptoms or shortness of breath, usually right after eating. Which food it is becomes clear from separate IgE tests together with the history of the symptoms. Without symptoms, no treatment follows.

Negative result

A negative result means that no IgE antibodies against the 6 foods were found. An IgE-mediated allergy to egg, milk, cod, wheat, peanut or soy is then less likely, but not completely ruled out: with soy and wheat the test misses some allergies according to the FMS guideline, and young children can react to cow's milk without detectable IgE. Other foods, such as nuts, sesame, shellfish or fruit, are not in the mix. Food intolerances such as lactose intolerance and celiac disease are not tested with this test.

After an abnormal result

The GP mainly looks at the history: which food, which symptoms, how soon after eating and how often. With a positive result, separate IgE tests follow if needed to see which food it is, often together with a food diary or temporarily leaving out and then reintroducing the suspected food. With a suspected real allergy or after a severe reaction, referral to an allergist or pediatrician follows, where a food challenge is done if needed.

Reliability

How reliable is the test?

A positive IgE result shows sensitization, not allergy: it only says that there are antibodies, not that you get symptoms from that food. The Dutch medical specialists' guideline (FMS) on food challenges advises against IgE tests for many foods at once and food mixes if there is no suspicion based on a good history of the symptoms, and calls a supervised food challenge the gold standard. A mix tests more allergens at the same time, so a positive result without clinical meaning occurs more easily; especially for cow's milk and chicken egg, the IgE test is not very specific. The screen is therefore mainly a first step after a clear reaction: a negative result makes an allergy to these 6 foods less likely, a positive result calls for separate tests.

What can affect the result?

Sensitization without symptoms is common, also through cross-reaction with pollen, for example with soy; the result can only be interpreted together with the history of the symptoms.
The test does not say which food is the cause; that requires separate IgE tests.
With soy and wheat, the test can miss an allergy, because important allergens are missing or present in too small amounts in the test material.
Foods outside the mix, and symptoms that are not IgE-mediated such as lactose intolerance and celiac disease, are not tested.

Who it is for

Who is the test useful for?

Useful for

Useful after a clear reaction shortly after eating, such as itching in the mouth, hives, swelling, vomiting or shortness of breath, where one of these 6 foods may be the cause and it is unclear which. If it clearly concerns one food, a separate IgE test says more. With vague symptoms such as abdominal pain, tiredness or eczema without a clear link to a meal, and in people who eat these foods without problems, the test adds little; the FMS guideline then advises against screening.

How common is it?

Many people think they cannot tolerate certain foods, but a real food allergy is much less common than that suspicion. In young children, an allergy to milk or egg usually goes away by itself: according to Thuisarts.nl, an egg allergy has gone in about half of children by the age of 2, while a peanut allergy often remains. Sensitization without symptoms is much more common than the allergy itself.

Thuisarts.nl and the Dutch GP guideline (NHG) on food hypersensitivity and celiac disease; no Dutch prevalence figure has been checked

Drawbacks and risks

A positive result without a clear reaction can lead to unnecessarily cutting out foods, with a risk of a one-sided diet and, especially in children, of more rather than less allergy.
A negative result can give false reassurance with an allergy to soy, wheat or a food that is not in the mix.

Get tested