If a patient has a flatline result on a SIBO breath test and you treat as positive for hydrogen sulfide bacteria, is there a way to retest to make sure treatment is successful? Even though the breath test is not measuring for hydrogen sulfide, could you expect that a repeated breath test would show a normal result or at least a

Chris Kresser:  This is the problem with the hydrogen sulfide hypothesis and diagnosis: There isn’t really a surefire way to retest to make sure that the treatment is successful. What we do typically tend to see, I can tell you from my clinical experience, is exactly what you guessed might happen, which is that when you do the repeated breath test, it shows a result that’s more normal. What you’re hoping for is low levels of hydrogen and methane all the way through 90 to 120 minutes and then a little bit of an increase as the lactulose goes into the colon because that would be a truly normal breath test result. But you have to consider the whole clinical picture when you do the retesting. You have to consider their symptoms, as well as the test results and their history.

There was an interesting study that was just published a few days ago. They took a bunch of people with IBS, and they tested them for SIBO, using lactulose breath testing. And then they gave rifaximin to everybody, regardless of what their SIBO breath test results were, and then they measured who responded to rifaximin. What they found was really interesting. It was that a lot of people responded to the rifaximin within the IBS group, but there was no correlation between who responded to the drug and who had SIBO, according to the lactulose breath test. So the conclusion of the researchers was that rifaximin is very helpful for dealing with IBS, and a lot of people benefit from it, but lactulose breath testing is not a helpful way of determining who will benefit from antimicrobial treatment.

We talked in the gut section about some of the issues with lactulose breath testing, and this is just another piece of that puzzle. I still think it’s worth doing, and actually if you read the paper, you’ll see that the authors still suggest doing SIBO breath testing for a number of reasons, but it does also emphasize that clinical therapeutic trials and using your judgment as far as just continuing to treat with antimicrobials if you think a patient would benefit from it, even in the absence of clear test results, is a perfectly valid approach, and it’s one that’s being advocated by the latest research in the field and clinicians that are actively treating IBS and SIBO. So just keep that in mind.