What Do Your SIBO Results Mean?

What Do Your SIBO Results Mean?

So you finally took the plunge. You did the prep diet, you took the breath test, and you now have your small intestine bacterial overgrowth (SIBO) results in your hand. But what the heck do they mean?

First, you should ideally consult with a healthcare practitioner who specializes in SIBO when analyzing your results. If, however, you’re doing this alone, then hopefully the tools in this guide will help you interpret your test.

How the test works

The SIBO breath test does not directly measure the number of bacteria in the small intestine; rather, it measures the gases (hydrogen and methane) produced by the bacteria, indicating whether bacterial overgrowth is present and, if so, the severity of it.

The gas is measured in parts per million, so when you look at your results, you’ll see numbers with “ppm” next to them.

The test results are compiled in a table and a graph. They’re the same results, just presented in two different ways.

It’s important to be aware of your baseline result. This is the breath test result from the first of the 10 tubes you breathed into — before you drank the lactulose or glucose solution. If this baseline result is high, especially with the hydrogen, this indicates the test was done incorrectly.

Another thing to note is, until very recently, there wasn’t any official guidance. Interpretation came down to the doctor and the lab dealing with the results, so there is still some debate and variations between what is and isn’t a positive.


Having some hydrogen in the large intestine is normal, so when it comes to interpreting your hydrogen markers, look at the first two hours of the test, as the third hour is generally thought to be representative of the large intestine.

The main breath test interpretation guidance comes from “Hydrogen and Methane-Based Breath Testing in Gastrointestinal Disorders: The North American Consensus.” According to this study, a rise in hydrogen levels of at least 20 ppm from the baseline number within the first hour and a half would yield a positive test result. For example, a baseline of 2 ppm would need to rise to 22 ppm for the test to be considered positive.

However, this guidance carries the risk of false negatives because so many people with SIBO have slow gut motility, which means the glucose or lactulose solution would take longer to reach the large intestine.

As a result, leading SIBO doctor Allison Siebecker’s guidance is slightly different after spending years working with thousands of SIBO patients. For Siebecker, a positive for hydrogen would be the hydrogen levels reaching over 20 ppm in the first two hours, with or without a rise.

To demonstrate, say someone’s baseline was 5 ppm, and after 120 minutes it reached 25 ppm. This would be a negative according to The North American Consensus because it didn’t rise by at least 20 ppm within the first 90 minutes. In contrast, this would be a positive for Siebecker.

Her one caveat is that the baseline cannot be the highest result or above 10 ppm, so if the baseline was 25 ppm but decreased to 18 ppm over two hours, this would indicate that the test wasn’t done properly.


Methane is slightly different. With methane, we’re looking at the entire three hours. There has been some debate over the years, but at present, The North American Consensus rules that a reading of 10 ppm or above is a positive.

However, for Siebecker and many other SIBO doctors, if a patient suffers from constipation (a classic sign of methane production), they would see anything from 3 ppm to 9 ppm as a positive.

One thing to note with methane is that a high baseline is fairly common with a positive result, so you may see numbers such as 10 ppm or higher in that first result.

Hydrogen sulfide

So, what about the elusive hydrogen sulfide SIBO? While the breath test cannot detect this gas, sometimes we get what’s called a “flat line,” which can indicate the presence of hydrogen sulfide. Listen to this podcast to understand more.

A negative test

If you have a negative test, do not fear. False negatives are possible, and some doctors suspect that methane can be present in undetectable amounts. Small intestine fungal overgrowth could also be the culprit, so at this stage I would suggest working with a specialist, having a stool test, and doing further research.


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