SIBO breath test
- Appointment required
SIBO breath test with a glucose or lactulose load and measurement of hydrogen and methane. It is designed to investigate possible bacterial or methanogen overgrowth in the intestine with bloating, wind, diarrhoea or constipation, always interpreting the result together with symptoms and risk factors.
No prescription needed, appointment required
Results in 3-5 working days after the test
Breath sample. Includes: Lactulose or glucose breath test. See what it measures
What it is for
It is used to investigate whether abnormally early fermentation may explain persistent digestive symptoms. It can add information when there are factors that favour overgrowth, such as certain digestive surgery, anatomical abnormalities or motility disorders.
It is not a general test for any kind of bloating. The symptoms of SIBO overlap with irritable bowel syndrome, coeliac disease and intolerances to different sugars, and the result must fit with the rest of the assessment.
When it is recommended
- Persistent abdominal bloating, wind or diarrhoea with risk factors for overgrowth
- Significant constipation when methane production is to be assessed
- Compatible symptoms after digestive surgery, including bariatric surgery
- Known motility disorders or anatomical abnormalities of the intestine
- Symptoms attributed to several food intolerances that do not fit a single sugar
Clinical comment
We measure hydrogen and methane because not everyone produces the same gases. Methane is not produced by bacteria but by archaea; that is why a raised result is more accurately called intestinal methanogen overgrowth, and it is linked mainly to constipation.
The breath test has limitations. Lactulose can reach the colon early in people with fast transit and mimic an early rise. Glucose may miss overgrowth confined to more distal segments. Bear in mind that a single positive result does not show that SIBO is the cause of all the symptoms.
We have kept both gases in the protocol because measuring hydrogen alone can leave a methane pattern unidentified. Even so, the indication and the clinical interpretation matter as much as the curve.
Dr. Antonio Mas
What is tested
• Lactulose or glucose breath test (exhaled hydrogen and methane): Measures both gases at intervals after taking the substrate. An early rise in hydrogen may point to SIBO, while raised methane is linked to overgrowth of methanogenic microorganisms and constipation.
- Lactulose or glucose breath test (exhaled hydrogen and methane)
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, prokinetics or probiotics 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.
- General blood testA general blood test with full blood count, glucose, cholesterol and kidney and liver function: the basic parameters included in any general check-up.+€59.00
- General + nutritional blood testEverything in the general blood test (anaemia, kidneys, liver, cholesterol and glucose) plus iron stores, vitamin D, vitamin B12 and folic acid. It is the broadest add-on: it covers the general and the nutritional in one go.+€129.00
- Coeliac disease antibodiesMeasures the antibodies used to investigate coeliac disease; for a reliable result, it must be done while you are still eating gluten.+€39.00
- Iron and anaemia studiesDistinguishes between iron deficiency, anaemia and vitamin B12 or folic acid deficiency, which call for different approaches.+€49.00
Related blood tests
We have other profiles in Digestive with more or fewer tests:
- Sorbitol intolerance test€60.00
- Fructose intolerance test€60.00
- Lactose intolerance test€60.00
- Helicobacter pylori breath test€69.00
- Coeliac disease blood test (antibodies)€69.00
- Vitamin B12 blood test€89.00
- Vitamin B12 blood test with antibodies€149.00
- Methylmalonic acid, for borderline B12 deficiency€149.00
- Coeliac disease genetic test (HLA DQ2/DQ8)€229.00
- Gut microbiota test€359.00
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
Recommends measuring hydrogen, methane and carbon dioxide together, because some people have gut flora that produces methane, and in them a recording that only looks at hydrogen comes back negative. It sets a positive methane result at 10 ppm and the load at 75 g of glucose or 10 g of lactulose.
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.