Do you really have SIBO? I often hear horror stories about people who can never clear SIBO. However, I rarely see this in the clinic. Part of the reason for this might be because the most popular SIBO test can cause what’s known as a false positive. This is when you don’t actually have SIBO but the labs say you do. It’s important to understand this so you know when you can stop SIBO treatment and so you don’t have to follow a SIBO diet forever.
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Do You Really Have SIBO?
Dr. Michael Ruscio: Hi. This is Dr. Ruscio. And let’s talk about SIBO (small intestinal bacterial overgrowth) to know when you have it and, more importantly, when you don’t have it.
SIBO, or small intestinal bacterial overgrowth, is a condition of bacterial overgrowth that may cause many of the cases of irritable bowel syndrome, or IBS. And this can include things like abdominal pain or gas; altered stool frequency or consistency—so constipation, diarrhea, and oscillation between the two; and also altered formation of the stool—loose stools, hard stools, compact stools. This is a common condition. IBS affects about 10% of the population. And SIBO (small intestinal bacterial overgrowth) can underlie many of those cases. So because of this, SIBO is often tested for.
And there are two different types of tests that can be used. They’re both breath tests. One uses lactulose. One uses glucose. And they both have merit. And they can both be used very successfully. But there are some intricacies to especially the lactulose test that are important to understand to prevent you from having what’s called a false positive. And this is where the lab says you have SIBO but you actually don’t have SIBO.
And what I’ve been noticing over the past year or so is many patients come in with quite a bit of fear surrounding SIBO. They’ve heard that you can never get rid of it. They’ve heard of people that keep treating it and retesting and are still positive. And I have not found that to be true for most cases. There is certainly a smaller subset of patients that have a very hard hand that they’ve been dealt.
And they have to work very hard to gain symptomatic improvement. And they’re much harder cases. But for the majority of people, SIBO is something that can be overcome. But if you don’t understand how to treat SIBO the right way (a), and also (b) understand how to interpret the tests, you can fall into the syndrome of thinking you’ve never been able to clear SIBO.
Now, recently in one of our podcasts we went into great detail comparing the lactulose and the glucose tests. And I’ll try to find that link and put that in here if you want to go to that episode and get all the science behind these different tests. But the main thing to understand is that with lactulose testing, there is a higher chance of having a false positive, meaning you’re falsely positive, meaning the test shows you have the condition but you don’t actually have the condition.
And one of the keynote things that can suggest this is if someone first has SIBO—again, all this will be on the lactulose test I’m referring to. Someone tests positive for SIBO. They treat it. And they respond very well to treatment. But their retesting shows they still have SIBO.
And especially if that retesting is done once and then maybe you do it again a month later or if you finish SIBO treatment and then your retest was several weeks later and you retested and your symptoms were still gone at that point, as long as there have been a few weeks where you’ve been symptom free and the retest shows that you actually have SIBO, that can denote a false negative.
And so I’ll put up on the screen in a minute here a patient’s lab results just from today that perfectly encapsulated this. But essentially, this gentleman came in with quite a bit of symptoms. He was also positive for SIBO. We treated him. He responded marvelously. Symptoms were pretty much completely gone, was feeling great. And we retested. His SIBO was positive. We decided, since this looked fishy, to wait a few weeks and retest again to see if that positive result was still found. And it was still found again.
So this gentleman, still feeling great and exhibiting none of the signs and symptoms of SIBO, came in feeling like he was a failure, he was doing something wrong, and he had this underlying problem. And he was actually very upset—excuse me—until I simply explained to him the issue of false positives.
And this is important because understanding the issue of false positives and explaining that to a patient can prevent them from thinking that something is wrong with them or they failed or they’ve done something wrong or they’ve eaten the wrong way. And it can take a lot of stress off them. And it can also prevent the clinician from needing to treat the patient again and more importantly treat the patient unnecessarily.
So to put this patient’s lab results up on the screen, here is what you see. You see there are samples 1, 2, 3, 4, 5, 6, 7, and so on. And they coincide with a time-interval-like baseline, 20 minutes, 40 minutes, 60 minutes, 80 minutes, 100 minutes, and so on. And then next to that, you see the ppm H2, which is just parts per million of hydrogen. And you also see ppm CH4, which is parts per million of methane. I’ll be referencing just the hydrogen for our conversation, the H2, because they both coincide with each other.
So when you drink the lactulose as part of this breath test, after you drink it, the lactulose works its way down your small intestine. And very little gas should be released there. But eventually when it gets into the large intestine, that’s where there’s a lot of bacteria and a lot of gas should be released. And we should see the levels elevate.
So around 100 to 120 minutes is when this transition should occur. This is why you see that black line between 7 and 8. That’s probably the latest point at which we’d expect this transition to occur. Now, that’s when we normally would see the gas levels elevate.
But in this patient, they’re elevated before that black line, which shows a positive. However, they’re only elevated kind of toward the end of this test, which could mean that that person has either a short small intestine or the lactulose is making its way through their small intestine too quickly, maybe because the lactulose is somewhat irritating to this individual’s small intestine.
So the small intestine rushes it through. It gets to the large intestine earlier than we think it should from a timing perspective. And we see this elevation of gas. So that’s what we’re seeing here. At 80 minutes and 100 minutes, we’re seeing the score of 109 and 119. But because this has happened in a patient who has for several weeks been symptom free, this is almost certainly a false positive.
So why this is important to understand is that, again, this prevents the patient from feeling like they did something wrong or there’s something wrong with them. It prevents the doctor from doing more or unnecessary treatment.
This doesn’t happen with glucose as a testing agent. So if you really wanted to verify this, you could repeat the test using glucose instead of lactulose. The patient and I today decided not to do that because really we had gotten to the clinical endpoint we were trying to get to. He was feeling much better. There wasn’t a need to do anymore testing.
This is not to say that lactulose is a bad test and can’t be used. It definitely has utility. It’s just important to understand this presentation. If someone has been treated and responded really well and their labs look like this with lactulose, meaning they’re positive but they’re only positive toward the end of the test, that’s very suggestive of a false positive.
So something very important to keep in mind, and I think this may prevent some people out there that I hear about indirectly in the clinic who claim they can never get rid of SIBO. It may be because you’re not working with a good clinician. It may be because you’re using an unvalidated test like potentially a urine test. Or it may be because you’re using a test, like the lactulose breath test, that has a high incidence of false positives.
At the end of the day, it’s important to be practical and think through these issues. If you’ve seen a great improvement in your symptoms, but your labs haven’t improved, I would always trust the symptoms ahead of the labs in most cases. It’s not an absolute rule. But certainly this case supports that.
So lactulose and glucose can both be used for SIBO breath testing. But lactulose has a much higher incidence of false positives. Be on the lookout, if you’re a patient or if you’re a clinician, for this type of presentation.
The short takeaway is if you see elevations of the gas levels only toward the very end of the test in a patient that has no symptoms or their symptoms have responded very nicely, then it’s most likely a false positive.
A little bit deeper of a concept than we usually discuss, but I think this hopefully will help a lot of people. So this is Dr. Ruscio. I hope this information helps you get healthy and get back to your life. Thanks.
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