Testing for intolerances: which test answers which question

22. Juli 2025 ca. 30 Minuten

What to expect in this article

1. What the word “intolerance” encompasses
2. How common the individual causes actually are
3. What a test result proves and what it doesn’t
4. When symptoms should first be assessed by a doctor
5. Three common assumptions and what the evidence shows
6. Lactose: when an enzyme is missing
7. Three tests, three different questions
8. Celiac disease: why gluten must stay on the plate before testing
9. IgE-mediated allergy: what a test result shows
10. Who might be a candidate for an IgE test, and who is not
11. IgG tests for foods: what you need to know
12. From suspicion to a useful diagnosis
13. What a home finger-prick blood test covers
14. Limitations: what testing for intolerances cannot do
15. What ultimately matters when testing
Frequently asked questions
Sources

What the word “intolerance” encompasses

People who want to test for intolerances usually have a very specific question in mind: Which food is causing my symptoms? It is a valid question. It just cannot be answered with a single test, and that is because of the word itself.

“Intolerance” is not a medical diagnosis, but an everyday description. It says that something happens after eating. It says nothing about what is going on in the body. But that process determines which test can detect anything at all.

Three processes that go by the same name in everyday life

The first process is a matter of digestion. A sugar from food is not broken down and absorbed, or is only partially broken down and absorbed. It travels on to the large intestine, where bacteria ferment it. The immune system is not involved. The best-known example is lactose.

The second process is an autoimmune disease. In celiac disease, after exposure to gluten, the immune system attacks the lining of the small intestine. The Institute for Quality and Efficiency in Health Care (IQWiG) describes it as gluten not being tolerated “and causing inflammation of the intestinal lining” (IQWiG, 2022).

The third process is a true allergy. Here, the immune system produces class E antibodies, or IgE, against a protein in food. The reaction usually starts quickly and can be triggered by even small amounts.

These three processes have little in common beyond the trigger. They differ in the amount that causes symptoms, how quickly the reaction occurs, and above all, what can actually be detected.

Why search engines lump everything together

The search for a test doesn’t start with a technical term, but with a gut feeling. That’s why people with four different causes for their symptoms end up searching the same term, and all see the same offers.

The fourth case belongs here, even though it is harder to pin down: sensitivity to wheat without celiac disease or an allergy. The IQWiG describes it as “sensitivity to components of wheat that does not, however, lead to pathological changes in the intestinal lining” (IQWiG, 2022).

There is no laboratory test to detect this fourth case. The IQWiG states: “If wheat sensitivity is suspected, it is important to first rule out celiac disease or an allergy.” (IQWiG, 2022) So the approach is to rule those out, not to use a test of its own.

What this means for choosing a test

That reverses the order. The test doesn’t tell you which cause is present; the suspected cause determines which test is even appropriate. That may sound inconvenient, but it saves money and weeks.

If the symptoms seem to come more from the digestive tract and are less tied to individual foods, it’s worth taking a different look first. You can look up which bacterial species and markers may appear in a stool test in the gut glossary.

How common each cause actually is

The rates vary widely, and that gap itself indicates where it makes sense to start investigating. Three figures from three reliable sources are shown side by side, each as a proportion of the population.

Three causes, three orders of magnitude

Source: IQWiG 2024 and 2022, DGAKI and other professional societies 2021

The figure for food allergies comes from the professional guideline of the allergy societies. It states verbatim: “A 2004 study found a prevalence of food allergy, confirmed by double-blind, placebo-controlled food challenge, of 3.7% in adults and 4.2% in children.” (DGAKI and other professional societies, 2021)

The note about the challenge test supports this statement. It refers to administering the suspected food under medical supervision in a controlled setting, without the participants knowing who gets what and when. Figures based solely on surveys are regularly much higher than those from such tests.

Why the lactose figure varies so much

The range for lactose stands out, and there is a geographical reason for it. IQWiG states: “About 5% to 15% of people from Europe cannot tolerate lactose.” (IQWiG, 2024) The same source gives entirely different figures for other regions of the world.

It says: “In Africa or East Asia, by contrast, 65% to over 90% of adults are affected.” (IQWiG, 2024) So, worldwide, people who can still digest lactose in adulthood are more the exception than the rule.

For the question of testing, this is more than a side note. Symptoms after consuming dairy products are not uncommon in Europe, but they are not the norm either. They are common enough to check for first, before starting more elaborate procedures.

What a test result does and does not prove

A lab result is a measurement, not a diagnosis. This distinction is the most important point in this entire topic, and it is stated so clearly in the professional guideline on food allergies that it belongs here verbatim.

The sentence consists of two parts, and the second is more important in practice. A positive result does not prove that this food causes your symptoms. And by itself, it is no reason to permanently remove it from your diet.

Sensitization means the immune system has produced antibodies. Whether this leads to a reaction depends on the symptoms, not the lab results. People can have measurable antibodies and eat without symptoms throughout their lives.

The reverse is also not clear-cut

An unremarkable result also isn’t an all-clear in the strict sense. The guidelines put it this way: “The absence of evidence of sensitization (negative specific IgE/skin prick test) frequently, but not reliably, rules out a clinically relevant IgE-mediated food allergy.” (DGAKI and other professional societies, 2021)

Common, but not certain. Two words that mark the difference between a clue and proof. If you still react after a negative result, you haven’t received a false result; you’ve received an incomplete answer.

What the evaluation actually begins with

That’s why it starts not with a test tube, but with a conversation. The guidelines put this at the beginning of their diagnostic chapter: “A detailed medical history should form the basis for diagnosing food allergies.” (DGAKI and other professional societies, 2021)

Medical history means what you ate, how quickly the reaction occurred, what it looked like, and how often it has happened. A test helps interpret these observations. It doesn’t replace them.

When symptoms should be evaluated by a doctor first

Before ordering any test, the first question is whether the symptoms are even consistent with an intolerance. Some signs answer this question on their own, and the answer is no.

Blood in your stool should be evaluated by a doctor. Unintentional weight loss should be evaluated by a doctor. Persistent fever should be evaluated by a doctor. Symptoms that wake you up at night should be evaluated by a doctor.

There is also a sign that is specific to this topic. A reaction that occurs within minutes and affects the skin, breathing, or circulation is not a case for an online test; it’s an emergency. Swelling in the mouth and throat, difficulty breathing, and circulatory problems after eating require immediate medical attention.

These signs are not a reason to try an elimination phase or place an order. They are a reason to make an appointment. If you notice them, don’t test—see a doctor.

The reason is that other causes are ruled out

Digestive symptoms after eating can be caused by conditions that have nothing to do with food. A test for antibodies to foods looks for something else and therefore won’t find them.

This is the real harm of testing at the wrong time: it answers a question no one asked and provides reassurance about one that remains unresolved. An unremarkable result can lead to a necessary appointment being postponed for months.

Three Common Assumptions and What the Evidence Shows

Three ideas come up again and again in conversations about this topic. All three are understandable, and all three contradict what professional societies and institutes have published on the subject.

Assumption and evidence

All three assumptions share the same core idea: they expect the lab to provide an answer it cannot give. In each case, the path forward involves observing your own daily life and choosing the right procedure.

Lactose: when an enzyme is missing

An enzyme breaks down lactose in the small intestine so that it can be absorbed. If there is too little of the enzyme, the sugar passes into the large intestine. There, bacteria ferment it, producing gas.

This explains the typical symptoms. IQWiG describes it this way: “After consuming milk and products containing lactose, many people experience digestive problems such as abdominal pain, bloating or diarrhea.” (IQWiG, 2024)

The amount is what matters. IQWiG notes that people who have difficulty digesting dairy products “may tolerate only small amounts” of lactose (IQWiG, 2024). So it is rarely a matter of a complete ban, but rather of finding an individual threshold.

Why a breath test measures it, not a blood test

Since no antibody is involved, there is no antibody to measure. Instead, the test measures the gas produced during fermentation and exhaled through the lungs.

IQWiG describes the procedure as follows: “Breath test: After drinking a lactose solution, the hydrogen content in the breath is measured several times.” (IQWiG, 2024) Several times is the key phrase here, because the pattern over time provides the information, not a single reading.

This test is done in a medical practice and takes time. That is the price of measuring the process in question. An antibody level in the blood cannot reflect this process, no matter how many foods are listed in the report.

Our article Recognizing lactose intolerance explains how you can investigate the question in everyday life before an appointment. This article focuses on which method identifies which cause.

What the source material says about other sugars

Alongside lactose, fructose is also frequently mentioned when discussing symptoms after eating. The source material reviewed for this article contains no specific information on this topic with an institution and year cited.

That is why no figure or description of a method is included here. If fructose is suspected to be the cause of your symptoms, discuss it at the same practice that offers the lactose breath test, rather than relying on an antibody result.

Three methods, three different questions

The following overview compares the three approaches using the same criteria. It does not rank them by effort or cost, but by which question each method answers and which questions it leaves open.

The fourth column is deliberately missing from this table. Tests for IgG antibodies to foods do not belong alongside these three methods, because they do not answer a question that these three leave open. Chapter 11 explains why.

Celiac disease: why gluten stays on the plate before testing

Celiac disease is the exception among the three causes, and it is the only one for which incorrect preparation can make the result unusable. That is why it gets its own chapter here.

On how common it is, IQWiG states: “About 1 to 2% of people in Europe have diagnosed celiac disease.” (IQWiG, 2022) It is rare enough to be overlooked, and common enough to be one of the possibilities when symptoms persist.

Two tests that belong together

The first step is a blood test. According to IQWiG, it looks for “immunoglobulin A (IgA) antibodies against a specific enzyme called tissue transglutaminase (tTG or TG2)” (IQWiG, 2022).

The second step examines the tissue itself. IQWiG explains: “In addition to the blood test, tissue samples are usually taken from the upper small intestine during a gastroscopy.” (IQWiG, 2022) Only the two steps together support the diagnosis.

This also makes clear what an antibody result alone can and cannot do. It is a clue that points the way forward. A diagnosis only emerges in a medical context, and that context cannot be established at home.

The most common mistake

If you suspect gluten, it may seem natural to stop eating it immediately. That is precisely the mistake. IQWiG states: “The test is only meaningful if enough gluten has been consumed beforehand.” (IQWiG, 2022)

The reason lies in how the tests work. Both look for a reaction to gluten. If the trigger is absent for weeks, antibody levels fall and the lining of the intestine heals. The results may then appear normal even though celiac disease is present.

If you already eat gluten-free but still want clarity, discuss the order of steps with a doctor before testing. Reintroducing gluten on your own is not a good idea if your symptoms were severe before. For a more detailed overview, see our article Celiac Disease Test.

IgE-mediated allergy: what a test result shows

A true food allergy is the only one of the three pathways in which an antibody in the blood actually corresponds to the process. That is why measuring IgE is an established diagnostic method here, not merely an indication.

The clinical guideline describes the diagnostic process as a combination of several building blocks: medical history, evidence of sensitization through specific IgE or a skin prick test, assessment of clinical relevance, and, if needed, a challenge test (DGAKI and other professional societies, 2021).

The test result is therefore one of several building blocks. It comes early in the process because it can be measured broadly and with little effort. It does not come at the end, because it cannot answer by itself what the result means in everyday life.

Why a positive result does not yet justify a diet

The statement from Chapter 3 bears repeating here because it has practical implications. Evidence of sensitization “should not on its own lead to therapeutic elimination” (DGAKI and other professional societies, 2021).

Here, elimination means permanently avoiding the food. If you do this based on a single result, you may cut out something you can tolerate without any problems. For children and staple foods, this can create a problem of its own.

Conversely, a result showing many abnormal values does not mean you have many allergies. It initially means that your immune system has reacted to several proteins. Which of these matter in everyday life is determined by considering your observations as a whole.

Cross-reactions as a common explanation

Some abnormal results for foods are due to similarities between proteins. People who react to certain pollens may also react to related proteins in fruit or nuts because their structures are similar.

For you, this means that a test result can explain why an apple makes your mouth tingle in spring but not in winter. An allergy specialist can interpret patterns like this. A number on its own cannot.

Who might benefit from an IgE test, and who might not

Whether a specific IgE test will help you depends less on how severe your symptoms are than on their nature. The following comparison gives genuine reasons for both sides.

Our article How much does an allergy test cost explains what an allergy test costs in a doctor’s office and laboratory and how it is performed. If you’re concerned about digestive symptoms rather than individual foods, At-home gut test explains the available procedures, and Diet for irritable bowel syndrome describes what the guidelines say about nutrition.

IgG tests for foods: what you need to know

One procedure is missing from the overview in Chapter 7, and it is precisely the one most often advertised online: testing for IgG-class antibodies against many foods at once. This omission is no accident.

IgG is a different class of antibody from IgE. Both belong to the immune system, but they represent different processes and must not be read as two variants of the same test. An IgG result is not an allergy test, and an allergy test is not an IgG result.

Allergy societies have issued a joint statement on these tests. Their assessment reads: “Therefore, allergen-specific detection of IgG or IgG4 antibodies against foods is unsuitable for the investigation and diagnosis of food intolerances and should be strictly rejected.” (Kleine-Tebbe et al., Allergo Journal, 2009)

The statement is based on a report by a working group of the European Academy of Allergy and Clinical Immunology and was adopted by the specialist societies in Germany, Austria and Switzerland. So this is not an individual opinion.

The disclaimer we put before every text on this topic

Allergy societies do not recommend IgG tests for diagnosing food intolerances. Elevated IgG levels indicate contact with a food, not necessarily an intolerance.

That is the key point for interpreting a result like this. An elevated value shows that your body is familiar with the food. For foods you eat often, that is normal and not a warning sign.

At most, such a result can serve as a starting point for a structured food diary: an indication of which foods to observe first during an elimination phase. This is most useful with the support of a nutrition professional. It does not establish anything or prove anything.

This assessment leads to an editorial decision that should be stated openly here: this article contains no offer or link for IgG tests. An article that cites professional societies’ assessments while also offering the relevant product contradicts its own position.

From suspicion to a useful result

Several weeks lie between the first suspicion and a reliable answer. This is not a sign of an unnecessarily complicated process, but the price of ending up with a result you can actually use.

The second step is the one many skip because it looks like a detour. It is the shortest route to the right test, because it narrows three possibilities down to one.

A diary that only lists foods is of little help. It becomes useful when, alongside what you eat, you record the time, the type and severity of the symptoms, and anything else that shaped the day. Four weeks is a good timeframe, as it can also reveal fluctuations unrelated to food.

What an at-home capillary blood test covers

mybody®x (MYBODY Lab GmbH) offers a capillary blood test for the third of the three pathways, namely IgE-mediated allergy. Before introducing the product card, the limitation needs to come first.

The test measures specific IgE. It therefore answers neither the question of an enzyme deficiency nor that of celiac disease. There is no equivalent product in the range for the lactose breath test, and a self-test for celiac disease does not replace the two-step medical assessment based on blood results and a tissue sample.

And the sentence from Chapter 3 also applies to this result: Evidence of sensitization does not prove the clinical relevance of the food tested. The price is as of 27/08/2026.

What a result like this is useful for in everyday life

It is most useful as preparation. Anyone who visits a practice with a result and a diary brings two things that would otherwise have to be collected there first. This does not shorten an appointment, but it makes it more focused.

What it does not replace is the assessment itself. The clinical guidelines recommend combining the medical history, evidence of sensitization and, where necessary, a provocation test. The last step takes place under medical supervision for good reason.

Limitations: what testing for intolerances cannot do

The first boundary comes at the start of any honest assessment. None of the methods in this article is a treatment. A test measures, and what follows from the measurement is decided afterward.

The second boundary lies in the scope. Each of the three methods captures exactly one process. There is no method that covers all four cases from Chapter 1 at once, and claiming that it does is itself a warning sign.

The third boundary concerns the meaning of a result. According to the clinical guidelines, evidence of sensitization does not prove the clinical significance of the food tested (DGAKI and other professional societies, 2021). A result without a medical history is therefore only half the information.

The fourth limitation concerns wheat sensitivity. There is no lab test for it, only the process of ruling out celiac disease and allergy (IQWiG, 2022). If you’re looking for a test for this, you’re looking for something that doesn’t exist.

What matters most in the end when getting tested

Four causes and three methods suggest a simple order. Observe before testing. Cause before method. Conversation before ordering. Consider everything together before making a list of things to cut out.

What stands out is mentioned in none of the sources cited, yet follows from all of them: The professional societies are less interested in the result than in the question that comes first. They don’t say which result is right. They say what question a result can answer in the first place.

So the next step is smaller than you might expect, and it costs nothing. Get a diary and write down what you eat, when symptoms occur, and what they’re like for four weeks. This diary will determine which of the three methods is even an option for you.

It started with the question of which test can tell you what you can’t tolerate. That’s exactly why it’s worth taking the detour through the food diary: You’ll get an answer, but it won’t come from the lab alone.

If you’re not sure which of the three approaches fits your symptoms: The consultation is free, and it won’t try to sell you anything.

Frequently asked questions

Sources

1. German Society for Allergology and Clinical Immunology (DGAKI), together with other medical societies, Worm M, Reese I, Ballmer-Weber B, Beyer K et al.: Update to the guideline on the management of IgE-mediated food allergies, AWMF registration number 061-031, Allergologie, volume 44, issue 7, 2021 – register.awmf.org
2. Institute for Quality and Efficiency in Health Care (IQWiG): Lactose intolerance, gesundheitsinformation.de, as of November 6, 2024 – gesundheitsinformation.de
3. Institute for Quality and Efficiency in Health Care (IQWiG): Celiac disease (gluten intolerance), gesundheitsinformation.de, as of December 14, 2022 – gesundheitsinformation.de
4. Kleine-Tebbe J, Reese I, Ballmer-Weber BK, Beyer K, Erdmann S et al.: No recommendation for IgG and IgG4 testing for food products. Position statement by DGAKI, ÄDA, GPA, ÖGAI, and SGAI following adoption of the Task Force report of the European Academy of Allergology and Clinical Immunology, Allergo Journal 2009 – gpau.de

The statements on sensitization, medical history, negative findings, the diagnostic workup, and the prevalence figures of 3.7 percent in adults and 4.2 percent in children are from [1]. The information on lactose, how it differs from allergy, the breath test, and the proportions of 5 to 15 percent and 65 to over 90 percent are from [2]. The information on celiac disease, tissue transglutaminase, the tissue sample, gluten intake before testing, and the proportion of 1 to 2 percent are from [3]; the descriptions of wheat sensitivity are from the same institute’s review “Gluten and wheat: sensitivity, allergy, or intolerance?”, dated 14.12.2022. The assessment of IgG and IgG4 testing is from [4]. Information on price, testing scope, sample type, and laboratory is from the mybody®x product page, accessed on 27.08.2026; processing times follow the general requirements for blood tests. All sources were accessed and reviewed on 28.08.2026.