Food allergy test: what IgE blood testing does and does not show

An online food allergy test that scans a hundred foods costs a few tenners these days. The result comes back with wheat, milk and egg flagged in red. Exactly what you eat almost every day.

That is no coincidence. That is the whole story.

We sell blood tests, which is precisely why I say this out loud: those panels sell the feeling of an answer, and the feeling is the product. Blood testing with real diagnostic value in food complaints does exist. It just does less than the advertising promises.

What is a food allergy test exactly?

A food allergy test measures specific IgE in your blood: the antibody your immune system makes against one particular allergen, such as peanut, egg or hazelnut. You get a separate value per allergen, in kU/l. So the lab is not looking at food in general, but at individual proteins.

The Dutch Voedingscentrum describes the distinction plainly. In a food allergy, your immune system reacts to certain substances in foods. In an intolerance, something else happens: the body can react to certain foods without the immune system being activated at all.

That difference decides whether a blood test can measure anything. IgE belongs to the immune system, so it belongs to allergy. In an intolerance there is no antibody to measure, and therefore no meaningful blood value either.

A blood-based allergy test does not measure some general "food sensitivity". It measures one antibody, against one protein, at a time.

The Voedingscentrum estimates that roughly 1 to 4% of the population has a food allergy or a food intolerance. In children it sits at 4 to 6%. Far more people suspect they cannot tolerate something, and that gap is where the entire commercial testing market lives.

At Vitalcheck you can have specific IgE measured through the food allergy panel, a fixed set of common food allergens. For pollen, dust mite and pets there is the inhalation allergy panel.

Does an IgG food intolerance test work?

No. An IgG or IgG4 test against foods says nothing about allergy or intolerance. Back in 2008 the EAACI Task Force concluded that IgG4 against foods signals repeated exposure and immunological tolerance instead (PMID 18489614). For working up food complaints, that test is not relevant.

The mechanism is almost mundane. If you eat bread often, wheat protein passes your immune system often. You make IgG against it, not because something is going wrong, but because your body knows that protein and tolerates it.

And so wheat turns red on your result. So does milk. So does egg. An IgG-based food intolerance test finds exactly what you eat most, then sells it back to you as the cause of your symptoms.

That is the trap.

That is not only a European conclusion. UMC Utrecht rejects the IgG test too: it mainly shows which foods you have eaten before.

Do you come across the claim that you need "a reliable IgG test" to track down your food allergy? It is wrong, and it has been in print since 2008.

I would never order such a panel myself, not even out of curiosity. You buy a list of forbidden products, you start cutting things out for no reason, and the real problem stays put. The same goes for hair tests and bioresonance: they measure nothing that has anything to do with allergy.

Which methods have actually been studied and which have not is set out in the overview on food intolerance testing: what works and what does not.

Does a positive IgE result mean you are allergic?

Not automatically. A positive specific IgE means you are sensitised: you carry antibodies against that allergen. Sensitisation is not the same thing as allergy. sIgE tests are excellent at identifying a sensitised state, but a positive result does not always equate with clinical allergy (PMID 22201146).

In plain terms: your immune system has recognised the protein and made antibodies against it. Whether it also gives you symptoms is a second question. Only once those symptoms appear do you call it an allergy.

UMC Utrecht, a Dutch academic hospital, is open about how often this goes sideways. In roughly fifty percent of cases where the test detects an antibody, there is nonetheless no allergy.

Half of them. That is not a footnote, that is the heart of this test.

Picture two people, both with a specific IgE for hazelnut of 3.5 kU/l. The first gets a tingling mouth and swollen lips after a handful of hazelnuts. The second has eaten hazelnut spread for years without a single complaint.

Same number, opposite meaning.

Cross-reactivity explains part of those confusing results. If you are allergic to birch pollen, your immune system can mistake proteins in apple and hazelnut for pollen proteins, simply because they resemble each other. You then test positive for nuts while getting little more than an itchy mouth. UMC Utrecht names apple, hazelnut and peach as familiar examples.

Your symptoms decide what the result is worth. The test supports your story, it does not replace it. That is also why a raised total value says little about one specific food. What a raised level does and does not indicate sits in the article on what a raised IgE in your blood means.

Are your symptoms still unexplained while your IgE is negative? Other mechanisms can be at play, histamine among them. Which blood values actually say something there is covered in the piece on the histamine intolerance test. The background sits in our explainer on histamine intolerance and what your blood shows.

So what is the most reliable way to establish a food allergy?

A conversation first, a test second. The 2023 EAACI guideline starts with an allergy-focused clinical history: what did you eat, how fast did the symptoms come, what did they look like. Only then come specific IgE or a skin prick test. The reference standard remains the supervised oral food challenge (PMID 37815205).

That order also sits in the European guideline on food allergy and anaphylaxis: a test only gains meaning inside the clinical story (PMID 24909706). In the Netherlands your GP works from the NHG standard on food hypersensitivity and coeliac disease, which follows the same line.

A food challenge is never something you run on your own. Under a doctor's supervision you get an increasing amount of the suspected food, with emergency medication within reach. That supervision is exactly what makes the test responsible.

The Voedingscentrum puts it bluntly: do not start experimenting yourself with leaving out or deliberately eating certain products. So never test a suspected food on yourself at home.

Do you get shortness of breath, swelling of your lips, tongue or throat, or other signs of anaphylaxis? That is acute care. Call 112 or go to the out-of-hours GP post. Blood testing has no role at that moment.

When is blood testing useful for food complaints?

In two situations. When you suspect an IgE allergy after a clear reaction to one food, and when you want to rule out that something else explains your symptoms. Coeliac disease, anaemia or a deficiency can cause the same gut complaints and fatigue as a suspected food hypersensitivity.

Coeliac disease is the clearest example. It is not an allergy and not an intolerance, but an autoimmune reaction to gluten, and targeted blood testing for it does exist. The difference, and how it is tested, sits in gluten intolerance or coeliac disease.

IgE blood testing is therefore not your only route in that second situation. An iron value or a thyroid value often says more about persistent fatigue than any allergy test.

We sell blood tests, and we deliberately do not sell those IgG panels. In my experience people are left with exactly one thing after such a panel. A list of products they no longer dare to eat, and still no answer to their complaint.

I would never start with one of those panels myself. If you suspect a real allergy, start with your story and your GP, not with an online panel. To test in a targeted way, pick specific IgE through the food allergy panel, or build your own test with the custom blood test builder. Then discuss your results with your GP.

References

1. Stapel SO, Asero R, Ballmer-Weber BK, et al. Testing for IgG4 against foods is not recommended as a diagnostic tool: EAACI Task Force Report. Allergy. 2008;63(7):793-796. PMID 18489614.
2. Santos AF, Riggioni C, Agache I, et al. EAACI guidelines on the diagnosis of IgE-mediated food allergy. Allergy. 2023;78(12):3057-3076. PMID 37815205.
3. Muraro A, Werfel T, Hoffmann-Sommergruber K, et al. EAACI food allergy and anaphylaxis guidelines: diagnosis and management of food allergy. Allergy. 2014;69(8):1008-1025. PMID 24909706.
4. Sicherer SH, Wood RA. Allergy testing in childhood: using allergen-specific IgE tests. Pediatrics. 2012;129(1):193-197. PMID 22201146.
5. Voedingscentrum. Encyclopedia: food hypersensitivity. Available via voedingscentrum.nl.
6. NHG. NHG standard on food hypersensitivity and coeliac disease. Available via richtlijnen.nhg.org, with patient information on thuisarts.nl.
7. UMC Utrecht. How is a food allergy established? Available via umcutrecht.nl.
8. UMC Utrecht. Birch pollen related food syndrome: cross-reactivity between birch pollen and foods. Available via umcutrecht.nl.

Every blood test result at Vitalcheck includes a professional assessment by a BIG-registered doctor. A blood value is not a diagnosis: always discuss treatment decisions with your GP.