The Best Test for SIBO: High-Level Scientific Evidence

Glucose breath test vs. lactulose SIBO breath testing for SIBO.

Key Takeaways

  • Glucose breath tests are more accurate than lactulose breath tests for diagnosing SIBO.
  • Elevations of methane or hydrogen after 90-100 minutes usually show bacteria in the large intestine, which is normal. Misreading this can lead to false positives.
  • You don’t need to rely on imperfect SIBO testing for results;  lifestyle interventions, such as diet, probiotics, or an elemental diet, can lead to good progress with symptoms.

There are unquestionably dogmas in the SIBO community. I like to consider myself a part of this community, and I generally agree with most positions. However, believing the lactulose test is the best SIBO test is at odds with what the data show. What is the best test for SIBO (small intestinal bacterial overgrowth)? Let’s discuss.

In This Episode…

SIBO and IBS … 00:00:47
Best Breath Test for SIBO? Meta-Analysis Review … 00:02:15
Glucose Breath Test Vs. Lactulose Breath Test … 00:03:05
Breath Test for SIBO Study Conclusion … 00:03:47
Lactulose Breath Test Challenges … 00:07:09
Glucose Breath Test Advantages … 00:12:04
How Useful are Breath Tests for SIBO? … 00:12:40
Breath Testing for SIBO Bottom Line … 00:14:16

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What is SIBO?

Let’s start by defining SIBO. Small intestinal bacterial overgrowth (SIBO) is exactly what the name implies: An excess of bacteria in the small intestine. This has been correlated with IBS to varying degrees, but there’s definitely a trend showing a correlation between irritable bowel syndrome (IBS) symptoms and SIBO symptoms, like gas, bloating, abdominal pain, and altered bowel function. There may also be a correlation with things like reflux and just general indigestion.


Now continuing further, why is SIBO relevant to IBS? We know via the gut-to-other-areas-of-the-body connections—gut-brain, gut-joint, gut-skin—that IBS may correlate with fatigue and depression, as one example. We know that some therapies for SIBO may also help with various skin eruptions and potentially even joint pain.

Some other evidence is correlating small intestinal bacterial overgrowth with metabolic imbalances like being overweight, and having higher blood sugar and cholesterol.

So, it’s not a surprising contention to put forth that imbalances in the gut—in this case SIBO—may correlate with a myriad of various symptoms and conditions. This is why it can be very helpful to have a diagnostic test to tell you yes or no, I have small intestinal bacterial overgrowth.

Best Breath Test for SIBO? Meta-Analysis Review

Now SIBO isn’t the only ailment in the digestive tract. But if you’re going to pursue testing, then it begs the question, what is the best test for SIBO. Thankfully, a meta-analysis, which is a summary of all of the available high-quality data, has been published to give us a definitive answer as to what the available data say regarding what is the best test for SIBO.

The meta-analysis is entitled Breath Test for Small Intestinal Bacterial Overgrowth Diagnosis: A Systematic Review with Meta-Analysis.

Glucose Breath Test vs. Lactulose SIBO Breath Testing

The most practical and clinically available tests for diagnosing SIBO are two different types of breath tests. Before SIBO breath testing, someone either drinks a glucose solution or a lactulose solution, and they collect breath samples with an at-home test kit. They measure the levels of hydrogen and methane gas being produced in the small intestine. Which type of breath testing is best?

This is where there is debate. The results of this meta-analysis, the pinnacle of scientific evidence, points to the answer. To quote their results: “Glucose breath tests showed a sensitivity issue of 58% and a specificity of 83%.” Juxtapose that with the lactulose breath test, which has a lower sensitivity at 42 and a lower specificity at 70.

Sensitivity tells you if you were correctly diagnosed with the condition, and specificity tells you if you were correctly found not to have that condition. This is very relevant because one of the things I’ve grown increasingly concerned about in some of the natural health communities, is the degree to which patients are being incorrectly diagnosed with SIBO and subjected to unnecessary fear, dietary restrictions, and treatments of various sorts.

Things in the field are getting better as we enhance our understanding, but I think it’s fair to say that there are a number of patients who have been told they have SIBO when they likely do not.

This is likely because the lactulose breath test—while helpful in the hands of an astute clinician who is using it correctly—actually suffers from a higher number of false positives.

When we look at the meta-analysis data here, we see that the glucose breath test actually has better scores for sensitivity and specificity, meaning it correctly diagnoses those who have the condition, and it correctly identifies who does not have the condition more often.

The lower scores that you’re seeing for the lactulose test show that it is not as accurate. People who do not have SIBO are more often told that they have it, and people who do have SIBO are more often told that they do not have it.

Breath Tests for SIBO Study Conclusion

So this is pretty damning evidence for the lactulose breath test. It can be used, but let me share the conclusion of the researchers first: “Breath tests do not show excellent performance in comparison to the gold standard. However, keeping into account that SIBO is a benign disease that in most cases requires a simple antibiotic therapy, they can be considered as a surrogate test to replace the invasive one.”

So essentially, they’re saying the SIBO breath test is not perfect. However, given the fact that the gold standard test involves an endoscopy and sampling of fluid from the small bowel, which is quite invasive and really can’t be done in routine clinical practice, breath testing, though imperfect, is probably the most justifiable test.

In this context, the glucose breath test has a better sensitivity and specificity than the lactulose breath test and therefore should be preferred.

Lactulose Breath Test Challenges

Now my caveat: I think this is what the research will eventually come to bear out. One of the challenges with the lactulose breath test is in the time interpretation of the test.

So here is what a typical SIBO breath test result looks like. What’s important when looking at the lactulose breath test to identify at what point you’re no longer seeing the small intestine have readings at zero, and then usually at 15- or 20-minute intervals from there. Most labs will use the 20-minute interval, and so we have zero, 20, 40, 60, 80 and so on.

The preferred window is really 80 to 90 minutes. If you want to be extra liberal, you could go up to 100 minutes. When we get to the 80- or 90-minute point, that’s when we’re starting to see the transition to the large intestine in many cases. This matters because if you see the gas levels go up in the large intestine, this is actually normal.

Now, unfortunately, the SIBO lab analyzers haven’t really caught up with this interpretation just yet. So it’s incumbent upon the clinician to make this interpretation. The lab machines will oftentimes use 120 minutes as the cutoff. So people who have an elevation at 100 minutes or 120 minutes—and if a provider is really kind of liberal with their diagnosis, perhaps even at 140 minutes— are sometimes erroneously told they have SIBO. So if you’re more judicious with the time window with your interpretation of a lactulose breath test, in theory you can mitigate this false positive.

This is getting a little bit nuanced, but here’s why this is important: there will be a number of patients who will show this positivity towards the end of the test. Many of these patients actually do not have SIBO.

Now, to play devil’s advocate here, I can’t say definitively that every one of those cases will not benefit from therapy, and that’s kind of a different question. But if you’re using a lactulose SIBO breath test, it’s important to not be overly liberal in throwing around a diagnosis, especially if the only elevation of gases is seen towards the end of the test.

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Glucose Breath Test Advantages

The glucose breath test seems to protect against that false positive. I feel this is very important for patients to understand because unfortunately, this update hasn’t seemed to permeate the SIBO community. While I would assume any provider has the best intentions in attempting a diagnosis, it does seem that many patients are being told they have SIBO when they don’t. This is a problem because it subjects people to unnecessary fear, worry, and potentially dietary restrictions and treatments.

How Useful Are Breath Tests for SIBO?

The overall utility of SIBO breath testing is moderate. It can be helpful, it can help to steer decisions, but it’s not the end all, be all. We can test for many things in the gut, but there are just as many possible things wrong that we can’t test for. Just as a point here to reinforce this, we know that SIBO exists. We also know that small intestinal fungal overgrowth exists. This is something we’ve talked about in the podcast before with Dr. Satish Rao. However, routine testing is not available for that.

We can only test for about half of the imbalances we know exist in the small intestines, which is why I don’t think it’s in the best interest of a patient or in the best interest of a provider to overly focus on testing. We can use testing as part of the informative process to determine what may be going on with a given individual, but we can also use many therapies for treating SIBO, without needing any type of lab results. Probiotics are one example. They can be quite effective and helpful for small intestinal bacterial overgrowth.

We’ve previously discussed five clinical trials and one meta-analysis showing that probiotics can be an effective treatment for SIBO. You don’t need a breath test to use a probiotic for a SIBO or for your IBS symptoms. The same likely applies for SIFO, knowing that probiotics also have antifungal effects.

Breath Testing for SIBO: Bottom Line

So the picture I’m trying to paint here is that testing can be helpful, but it is imperfect. Of the SIBO breath tests, the better is the glucose breath test, although with a well-trained clinician, a lactulose test could be responsibly used. All that being said, I wouldn’t go to great lengths to perform testing. If you haven’t yet, try to improve your diet, try to use probiotics, potentially carefully use herbal microbial therapy, consider using an elemental diet.

All the things that I’ve laid out in Healthy Gut, Healthy You can really lead to quite a bit of improvement. A number of individuals we’ve spoken with, who’ve seen numerous doctors and not recovered their gut health and then gone through the simple protocol laid out in the book Healthy Gut, Healthy You have seen the results they’re looking for. That’s a testament to the fact that copious testing isn’t necessary in most cases. Rather, having a well-constructed clinical, stepwise process that’s very evidenced based and scientifically informed can actually work better—unfortunately, in many cases—than seeing a clinician.

Now, there’s certainly a time and a place for a clinician, and I do not want to dissuade anyone ever from checking in with their family doctor or their gastroenterologist, or going through the appropriate evaluations. That said, if you’ve had the appropriate evaluation and you’re still floundering, then Healthy Gut, Healthy You really does seem to offer some nice benefits. It’s a derivative of what I do in the clinic, combined with a pretty strong evidence-informed review.

So in any case, the two best tests that are readily available are glucose breath tests and lactulose breath tests. Thankfully we now have gold standard evidence from the meta-analysis that the glucose test is likely the better option. So this is Dr. Ruscio and I hope this information helps you get healthy, get back to your life. If you do perform breath testing for SIBO, you’ll be able to choose the one that is probably in your best interest.

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