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Digestive Disorders > Intolerances > Lactose Intolerance

Lactose intolerance test: How to test at home and at the doctor

Dr. med. André Sommer

Dr. med. André Sommer

Lactose intolerance is one of the most common food intolerances. It is believed that up to 20 percent of people in industrialized nations may suffer from the condition. Lactose intolerance can lead to gas, abdominal pain, and diarrhea but symptoms vary from person to person. That's why many people are wondering whether they actually suffer from lactose intolerance and how this suspicion can be confirmed. In this article, you will learn how to test for lactose intolerance and how reliable the common tests are.

What tests are there for lactose intolerance?

In order to understand what’s best to test suspected lactose intolerance, it is important to know the basics.

Lactose intolerance basics

Lactose (milk sugar) is a compound sugar, a so-called disaccharide. It consists of the individual sugars (monosaccharides) galactose and glucose together. The enzyme lactase breaks down lactose into its constituents in the intestine. Only the single sugars galactose and glucose can be absorbed by the intestine. On the other hand, the body cannot utilize unbroken lactose.

People who suffer from lactose intolerance have less lactase than healthy people. They cannot completely break down the lactose so it migrates to deeper parts of the intestine. Bacteria start to process the lactose there. This process gives rise to fermentation products, which include hydrogen, carbon dioxide, and short-chain fatty acids. An accumulation of these breakdown products leads to the typical symptoms of lactose intolerance:

  • Bloating
  • Stomach pain
  • Diarrhea

In order to diagnose “lactose intolerance”, a procedure in several stages is recommended. First, as with all food intolerances, an attempt should be made to narrow down the triggering food more precisely. Two processes play an important role here:

  • Intolerance self-test
  • Food diary

A self-test aims to narrow down the possible presence of intolerance. Such a self-test, which analyzes symptoms based on specific and carefully selected questions, can be carried out online, for example. If the suspicion of an intolerance is confirmed, you can use a food diary (e.g. the free Cara Care app) to figure out the triggering foods and situations more precisely.

These first stages are usually followed by detailed medical diagnostics. Among other things, the doctor will conduct a detailed anamnesis interview, carry out allergy diagnostics, and use various tests to diagnose “lactose intolerance”. These tests include

  1. Lactose provocation test
  2. Hydrogen breath test
  3. Genetic studies

How does the self-test for lactose intolerance work?

A self-test can help you to substantiate the initial suspicion of lactose intolerance by using carefully selected questions about symptoms and eating habits to check whether your symptoms fit the picture of lactose intolerance.

Is there a lactose intolerance self-test online?

Cara Care offers various free self-tests for food intolerance developed by doctors, including a test for lactose intolerance. With the help of the questionnaire, which can be filled out online in less than ten minutes, Cara Care creates an indicative evaluation that you receive immediately by email.

The lactose intolerance self-test is very reliable due to the carefully selected questions. However, it should always be carried out in addition to a medical examination, not as a replacement for it. For example, those affected can take the test before visiting a doctor to give the doctor help and as preparation for the doctor's consultation.

What if the self-test confirms lactose intolerance?

Lactose intolerance should only be confirmed by a medical professional. In order to support the results of the test, a food diary can help. In such a diary, each meal is recorded and associated with possible symptoms. This enables patients to have a good overview of their symptoms and their triggering factors and can provide further important information to their doctor.

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Are there any other self-tests for lactose intolerance?

It is possible to carry out a so-called “provocation test” at home. Basically, this is the controlled intake of lactose to provoke the appearance of symptoms.

It is important that such a test should not be carried out if you know you respond negatively to the consumption of milk and milk products or if you are already known to be lactose intolerant. And if you are allergic to milk or milk products (cow's milk protein allergy), you should not carry out the self-test.

How is the provocation test done at home?

It is best to do the test in the morning and on an empty stomach. Drink 250 ml milk in a short time. Then wait about 30-60 minutes and watch for symptoms such as abdominal pain, bloating, or diarrhea. If you observe these symptoms, you are likely to be lactose intolerant.

As an additional security, you can do a “blind” test with lactose-free milk. That means you additionally have 250 ml lactose-free milk on hand and then drink one of the glasses - without knowing whether it contains lactose-free or lactose-containing milk. Simply mark the glasses beforehand to see which milk you have chosen later. Then continue as usual and note any symptoms that arise.

After the test is finished, check which milk you have actually consumed. If you actually suffer from lactose intolerance, lactose-containing milk should trigger the symptoms, but lactose-free milk should not cause symptoms.

How do doctors test for lactose intolerance?

Various diagnostic tests are available to the doctor. First of all, the doctor will take your detailed medical history, within which she will carefully record your eating habits and symptoms, among other things.

An allergy history and testing should be performed, too. In this way, it can be ruled out that the symptoms are caused by a food allergy and not by a lactose intolerance.

In rare cases, the doctor will carry out a provocation test: the patient drinks a lactose solution that contains 25 grams of lactose. Then, similar to the self-test, the doctor uses a score to rate the patient's symptoms to decide if lactose intolerance is present. Instead of a provocation test, a so-called hydrogen breath test is often performed today.

There is also a genetic test for lactose intolerance. To carry out such a test, the doctor needs the patient's explicit consent. The test examines the genes responsible for the enzyme lactase. This allows the doctor to understand whether the enzyme is sufficiently available in the respective patient or whether there is a deficiency.

How reliable are home lactose intolerance tests from the internet?

Tests from a wide range of providers on the internet promise fast and reliable diagnosis. Most of the time these are expensive test kits that are used at home and then sent to a laboratory.

Although such tests can support suspected lactose intolerance, they never replace detailed medical diagnostics. At most, the tests can provide additional information about the presence of the disease. For patients, this often means that the test is costly but has no added value.

Ledochowski, M., Bair, H., & Fuchs, D. (2003). Laktoseintoleranz. Journal für Ernährungsmedizin, 5(1), 10-16. Online:

Terjung, B., & Lammert, F. (2007). Laktoseintoleranz: neue Aspekte eines alten Problems. Dtsch Med Wochenschr, 132(06), 271-275. Online:

Litschauer-Poursadrollah, M., El-Sayad, S., Wantke, F., Fellinger, C., & Jarisch, R. (2012). Bauchschmerzen, Blähbauch, Diarrhoe: Fruktosemalabsorption, Laktoseintoleranz oder Reizdarmsyndrom?. Wiener Medizinische Wochenschrift, 162(23-24), 506-512. Online:

Dr. med. André Sommer

Dr. med. André Sommer

I’m André, a medical doctor from Berlin. Together with a team of medical doctors, nutritionists and data scientists we empower people to understand digestive issues with our app Cara Care.

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