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Gut · Stool
Prevotella/Bacteroides ratio
The ratio between Prevotella and Bacteroides, two groups of gut bacteria that often take each other's place.
At a glance
- Measured in stool
- In 1 test panel
- No special preparation
Explanation
Prevotella/Bacteroides ratio: what is measured?
This ratio is calculated from the measured amounts of Prevotella and Bacteroides. In many people one of the two dominates; which one differs greatly between people and is linked to diet, among other things. A high or low ratio is not an abnormality. According to international experts, such rough measures can describe both a normal and a disturbed gut flora.
What can it detect?
- The composition of the bacteria in the stool at the time of sample collection
- Shifts in the gut flora (dysbiosis), a concept with no fixed definition and no established medical significance
Result
What does the result mean?
Prevotella/Bacteroides ratio too high
A value above the laboratory's reference value means that this bacterium, substance or calculated value is more abundant in this portion of stool than in the people the laboratory compares with. On its own, this says nothing about your health: the gut flora differs greatly from person to person and can change from day to day. Common harmless causes are your eating pattern, a recent course of antibiotics, acid-reducing medicines, probiotics, a recent stomach flu and loose or, on the contrary, hard stools. There are no symptoms that go with a raised value, and a raised value does not prove that symptoms are caused by the gut flora.
Prevotella/Bacteroides ratio too low
A value below the laboratory's reference value means that this bacterium, substance or calculated value is less present in this portion of stool or was not found. This too says nothing about your health on its own. A low value is common after a course of antibiotics, with little fiber in the diet, with loose stools or simply because of differences between people and between days. A low value does not mean that your gut is missing something that needs to be topped up, and there are no symptoms that go with it.
After an abnormal result
For the GP, an abnormal value in the gut flora is usually no reason for further tests or treatment. With symptoms, the GP looks at the symptoms themselves and, if needed, arranges tests according to the guideline, for example for celiac disease, bowel inflammation or a gut infection. According to international experts, the result is not a basis for a diet, supplements or antibiotics.
Reliability
How reliable is the test?
Gut flora testing describes which bacteria are in a portion of stool. It has not been shown that the result helps in making a diagnosis or choosing a treatment, in people with or without symptoms. According to the guideline on irritable bowel syndrome, there is no test that can confirm this condition. An international group of experts concluded in 2025 that there is not enough evidence to use gut flora testing in healthcare, that there are no fixed healthy reference values and that there is no generally accepted definition of dysbiosis. According to the MDL Fonds (Dutch digestive health foundation), too, we do not yet know exactly what a healthy gut flora is; the result is therefore a description, not a medical judgment.
What can affect the result?
- The composition differs greatly from person to person and can change from day to day; a second portion of stool can give a different result.
- Diet, antibiotics, acid-reducing medicines, laxatives, probiotics and a recent gut infection affect the result.
- Methods and reference values are not standardized; results from different laboratories or methods cannot be compared with each other.
- Stool mainly shows the bacteria in the last part of the large intestine, not those in the small intestine or on the gut wall.
Who it is for
Who is the test useful for?
Useful for
The result is a description of your gut flora at one moment, with no established medical significance, whether or not you have symptoms. The test is not needed to stay healthy and does not explain bowel symptoms. With bowel symptoms, the GP usually finds the cause through questions and a physical examination, supplemented if needed with targeted blood or stool tests, for example for celiac disease or bowel inflammation. With blood in the stool, unexplained weight loss or new bowel symptoms after the age of 50, this test is no substitute for an examination by the GP.
How common is it?
Because there is no fixed definition of an abnormal gut flora, there are no figures on how common it is. Bowel symptoms without a clear cause are common, though: according to the guideline, irritable bowel syndrome affects about 4 in 100 adults in the Netherlands (by the strictest criteria).
Dutch medical specialists' guideline (FMS) on irritable bowel syndrome (NHG and NVMDL)
Get tested
Prevotella/Bacteroides ratio: test panels
Prevotella/Bacteroides ratio is part of these test panels. You order online and have your blood drawn at a collection point or collect the sample at home.
Evidence
Sources
This explanation is based on Dutch guidelines and independent information. It is general information, not a diagnosis. Discuss an abnormal result with your GP.
More about risks and results- Porcari S, et al. International consensus statement on microbiome testing in clinical practice. Lancet Gastroenterol Hepatol 2025;10:154-67 (open-access versie, Wageningen University & Research)
- FMS Richtlijnendatabase: Prikkelbaredarmsyndroom, module Diagnostiek PDS
- NHG-Standaard Prikkelbaredarmsyndroom (PDS)
- Thuisarts.nl: Ik heb het prikkelbare-darm-syndroom (PDS)
- MDL Fonds: Alles over je darmmicrobioom
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