Lactose breath test – H₂ breath test for lactose intolerance

Milk sugar (lactose) is split into glucose and galactose in the small intestine by the enzyme lactase. If lactase is missing or reduced, unsplit lactose reaches the large intestine. There, bacteria ferment it, producing hydrogen among other things, which passes via the blood to the lungs and is exhaled (PubMed 31427404).

If hydrogen rises over time after the lactose solution, this can be an indication of lactose malabsorption, meaning that milk sugar was not fully absorbed. Which values count as conspicuous is shown in the report as the laboratory's reference range. Whether this amounts to lactose intolerance also depends on whether symptoms occur at the same time; the European guideline requires symptoms to be recorded during the test for this (PubMed 34431620).

In the gut, methane is produced not by bacteria but by so-called methanogenic archaea (PubMed 39147218). They consume hydrogen and convert it into methane. In some people, mainly methane rises after a sugar load and hardly any hydrogen. This is why the test measures both gases; the North American consensus on breath testing also assesses methane separately (PubMed 28323273).

Raised methane levels are observed more often in studies in people with constipation (PubMed 39147218). The methane value alone does not say anything about lactose intolerance.

Measurements are taken before the lactose solution (baseline) and 30, 60, 120 and 180 minutes afterwards. What matters is not a single value but the course over time: the report shows a curve for hydrogen and methane over three hours.

The baseline value is the starting point. If it is already high, this may be due, for example, to preparation not being followed, such as high-fibre food the evening before; the guidelines describe such confounding factors in detail (PubMed 34431620). That is why preparation is so important.

Yes. In people whose gut flora mainly produces methane instead of hydrogen, the rise in hydrogen may be absent; this is why methane is also measured. Conversely, an early rise may also come from bacteria in the small intestine; the North American consensus therefore advises considering small intestinal bacterial overgrowth (SIBO) to avoid false-positive results (PubMed 28323273). Antibiotics in the weeks before the test, laxatives or a recent colonoscopy can also change the gut flora and therefore the result. The guidelines name these influences as reasons for careful preparation (PubMed 34431620).

Specialists distinguish three terms: lactase deficiency means that the small intestine produces little lactase. Lactose malabsorption means that milk sugar is not fully absorbed. Lactose intolerance refers to symptoms such as abdominal pain, bloating or diarrhoea occurring after milk sugar (PubMed 31427404).

Not every case of lactose malabsorption leads to symptoms. Whether symptoms occur depends, among other things, on the amount of lactose, lactase activity and the gut flora (PubMed 31427404).

The ability to keep producing lactase as an adult is genetically determined and varies widely around the world: in Northern Europe most adults continue to produce lactase, while in parts of Asia and Africa only a minority do (PubMed 42345379). Worldwide, the frequency of lactose intolerance is estimated at around 57–65% (PubMed 33887513).

Besides this inherited form there is secondary lactase deficiency: it can arise when the lining of the small intestine is damaged, for example by infections or other diseases of the small intestine (PubMed 31427404). One example is coeliac disease.

There are several methods: the hydrogen breath test (H₂ breath test), a genetic test for the inherited ability to produce lactase in adulthood, a blood-sugar tolerance test and examinations of tissue samples from the small intestine (PubMed 31427404). The breath test is non-invasive and the method most commonly used in practice (PubMed 33887513).

A genetic test only shows the predisposition, not whether milk sugar is currently poorly absorbed; secondary lactase deficiency therefore goes undetected. The breath test, by contrast, measures what actually happens in the gut after a lactose load.

The breath test shows whether gases are produced after the lactose load that indicate fermentation in the large intestine. How well self-reported intolerance, the measured result and later dietary changes match varies between studies (PubMed 31427404). The European guideline therefore stresses that symptoms must be recorded during the test before speaking of “intolerance” (PubMed 34431620).

The report is therefore one building block. Interpreting it together with your symptoms belongs in a medical assessment or in the conversation with the ORY expert team or with your doctor or naturopath, for example from the ORY expert network.

After milk sugar, research mainly describes the following complaints in lactose intolerance, with varying strength of evidence:

• Abdominal pain, bloating and distension: part of the definition of lactose intolerance and well documented (PubMed 31427404).
• Diarrhoea: occurs because undigested lactose draws water into the bowel and is fermented; well documented (PubMed 33887513).
• Increased gas (flatulence): caused by bacterial fermentation, well documented (PubMed 42345379).
• Stronger symptoms in irritable bowel syndrome: people with a sensitive gut (visceral hypersensitivity) have symptoms more often at the same lactose dose, observed in studies (PubMed 31427404).
• Symptoms from other sugars: lactose is only one of several poorly absorbed carbohydrates that can cause symptoms in a similar way, such as fructose or sorbitol (PubMed 31427404).

These are associations from studies, not causes in an individual person. The test cannot explain symptoms and does not provide a diagnosis. Persistent symptoms should first be assessed by a doctor.

If you have blood in your stool or black stool, unintended weight loss, fever, diarrhoea at night, severe or new abdominal pain, persistent vomiting or difficulty swallowing, the first step is a doctor’s practice, not a self-test. The same applies if your bowel habits change for the first time from around the age of 50, or if inflammatory bowel disease, coeliac disease or bowel cancer runs in your family.

Symptoms after dairy that appear suddenly in adults who used to tolerate milk well may also have another cause in the small intestine and should be assessed by a doctor. For babies and young children with symptoms after milk, the paediatrician is the right place. A breath test does not replace bowel cancer screening.

This page does not give treatment advice. Whether a result means anything at all and which steps make sense depends on your whole situation: symptoms, previous findings, medication and diet. Reviews describe that the benefit of such measures may be limited because lactose is only one of several poorly absorbed sugars (PubMed 31427404).

What makes sense for you belongs in a conversation with the ORY expert team or with your doctor or naturopath, for example from the ORY expert network. The results consultation is included in the price.

Weeks before: any antibiotics should have been finished at least 4 weeks earlier; no colonoscopy in the last 4 weeks. 24 hours before: no laxatives, no enemas, no probiotics. Only pause prescribed medication after talking to your doctor.

The evening before: light food such as white rice, white bread, chicken, fish or eggs; no pulses, wholegrain products, onions, high-fibre or fermented foods and no alcohol. Then stay fasting for at least 12 hours, water only.

During the test: no food, no chewing gum, no smoking and no physical exertion for three hours. The tubes do not need to be refrigerated and are only sent from Monday to Thursday.

The test starts in the morning on an empty stomach and takes three hours. First you breathe into the tube for the baseline value: breathe in deeply, hold your breath for about 10 seconds and then breathe out completely. Then you drink the lactose solution provided within 5 minutes and note the start time. Another breath sample follows after 30, 60, 120 and 180 minutes. In between you can sit and rest at home.

At the end, you put all five labelled tubes in the prepaid return envelope.

The report shows the measured values for hydrogen and methane at all five time points, as a table and as a curve, each with the reference range stated by the laboratory. A sample report can be seen in the instructions. Interpreting the values belongs in the results consultation, which is included in the price.

The analysis usually takes 7–21 days from the time the sample arrives at the laboratory. You will be notified as soon as your report is ready. The results consultation with the ORY expert team is included in the price.

The lactose breath test costs €65 including VAT, shipping, return shipping within Germany and the results consultation.

Statutory health insurance in Germany does not usually cover breath tests that you order yourself. With private insurance, reimbursement may be possible; the process is described under “Reimbursement by private insurance”.

The lactose breath test (€65) measures the gases after a lactose load. For fruit sugar there is the fructose absorption analysis (€65). The hydrogen & methane breath test (€115) looks at gases produced early in the small intestine, a topic discussed under the term SIBO. For histamine there is the histamine stool test (€55), and for antibodies against gluten components the gliadin and transglutaminase stool test (€95).

Which test makes sense for you can be clarified in the free initial consultation.