Lactose intolerance test
- Appointment required
Lactose intolerance test using a breath test with a lactose load. It measures whether lactose is digested and absorbed properly and makes it possible to relate the hydrogen curve to bloating, wind, pain or diarrhoea appearing during the test.
No prescription needed, appointment required
Results in 3-5 working days after the test
Breath sample. Includes: Lactose breath test. See what it measures
What it is for
It is used to investigate whether symptoms that appear after drinking milk or eating other foods with lactose are due to malabsorption. It helps avoid unnecessary restrictions and distinguish between reduced tolerance to certain amounts and more marked maldigestion.
The test measures lactose malabsorption. To speak of clinical intolerance, compatible symptoms also matter. A positive curve without discomfort does not mean that all dairy has to be cut out, and the amount tolerated varies between people.
When it is recommended
- Bloating, wind, abdominal pain or diarrhoea after drinking milk or eating foods with lactose
- Recurrent digestive symptoms with an unclear link to dairy
- Before cutting out all lactose-containing products for a long period
- Suspected secondary intolerance after gastroenteritis or a bowel condition
Clinical comment
It is important to distinguish lactose intolerance from cow's milk protein allergy. The first is linked to insufficient digestion of lactose and usually causes digestive symptoms. The second is a different immune reaction and is not investigated with this test.
The curve must also be interpreted together with the symptoms and the preparation. Small intestinal bacterial overgrowth can bring fermentation forward and produce a misleading result. In addition, some people produce little hydrogen, so no breath test is perfect.
Bear in mind that a positive result does not usually mean that all dairy has to be cut out. Many people tolerate small amounts or lower-lactose products, and the dietary plan should be adjusted to actual tolerance.
Dr. Antonio Mas
What is tested
• Lactose breath test (exhaled hydrogen): After taking a standardised amount of lactose, it measures hydrogen in exhaled breath at intervals. If lactose is not digested well, it reaches the colon and is fermented by bacteria, which raises hydrogen.
- Lactose breath test (exhaled hydrogen)
How to prepare
An appointment and 12 hours of fasting are required, and you must follow the preparation diet set by the centre on the previous day. Do not take antibiotics during the 4 preceding weeks, or laxatives or prokinetics during the preceding week.
The test lasts between 2 and 3 hours and you must stay at the partner centre. Do not smoke or exercise during the hours before or during the test.
You can add
Without another needle. It is offered when you order, so you do not have to decide now.
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The most comprehensive is not always the most useful. Each profile page explains when it makes sense and when it does not.
What it is based on
Rezaie A, Buresi M, Lembo A, et al. · American Journal of Gastroenterology 112(5):775-784
Standardises the breath test for lactose maldigestion: it sets the load at 25 g of lactose with a glass of water and a collection period of at least three hours, which is how this test is carried out.
Protocol designed by Dr. Antonio Mas, specialist in Endocrinology and Nutrition, Spanish medical licence no. 080846289, and reviewed in September 2026.
This blood test is a standardised protocol and does not replace a medical consultation. If you have symptoms, a known condition or a complex clinical situation, speak to your doctor.