Dr. Michael Ruscio, DC is a clinician, Naturopathic Practitioner, clinical researcher, author, and adjunct professor at the University of Bridgeport. His work has been published in peer-reviewed medical journals and he speaks at conferences around the globe.
SIBO (small intestinal bacterial overgrowth) has become a very common condition lately, and it’s thought that many people suffering with IBS may actually have SIBO. Testing for SIBO can be a little tricky, and certain tests may have a high rate of indicating positive SIBO when the patient doesn’t actually have SIBO.
The gold standard for diagnosing SIBO is with a breath test that measures the levels of hydrogen and methane gas in your breath. Bacteria produce gases, and when there’s an overgrowth of bacteria in your small intestine, the gases can be measured through your breath.
If gas levels are above a certain number, then the test indicates a positive result for SIBO.
There are two types of SIBO breath tests based on the type of substrate that is used. Your doctor will order either a lactulose or glucose breath test. Upon taking the test, you will drink either the lactulose or glucose substrate, and then breathe into a bag every 20 minutes for three hours.
Which Version Is the Best?
The lactulose breath test is favored in the SIBO community. However, we’re now recognizing that lactulose can sometimes deliver a false positive—in other words, your test results indicate that you have SIBO when you really don’t. This happens because in some people, lactulose makes its way through the small intestine and into the large intestine very quickly.
Ideally, gas levels in the small intestine will be low, and you’ll naturally see them elevated in the large intestine where bacteria will feed on the lactulose. This would be normal and expected.
If lactulose makes its way through your small intestine too quickly and gets into the large intestine faster than expected, then you’ll get a false elevation of gas, resulting in a positive SIBO test when in fact you don’t really have SIBO.
The benefit of using lactulose is that it does travel throughout the small intestine and gives you a good indication of what’s going on in the distal portion of the small intestine. This is where SIBO typically resides.
The other option is to use the glucose breath test. Glucose does not produce the same false positive. If you get a positive result on a glucose breath test, you can feel confident that it’s an accurate positive result for SIBO. The downside is that glucose is rapidly absorbed, and it does not make its way to the end of the small intestine. If a person has SIBO in the distal portion of the small intestine, the glucose test may not catch it, and you’ll end up with a false negative.
What Does This Mean?
Let’s assume you’re a practitioner and you test a patient using the lactulose breath test. It comes back positive and you treat them. Their symptoms improve, but when you retest, their labs don’t improve. In this case, you may be seeing a false positive, and it’s likely unnecessary to continue treating them for SIBO.
This is especially important to explain to the patient or to understand if you are the patient. We’ve been noticing that many patients come to our clinic with quite a bit of fear around SIBO and with beliefs that you can’t really get rid of it. They hear of stories of people who continually treat SIBO but their test results are still positive. We don’t find this situation to be true in most cases.
For the majority of people, SIBO is something that can be overcome, but you must understand how to treat SIBO in the right way and understand how to interpret the test. Otherwise, patients can fall into a cycle of thinking they’ll never be able to treat their SIBO.
Understanding the issue of false positives and explaining it to a patient is important because it can prevent the patient from feeling like there’s still something wrong with them even though their symptoms have cleared. It also prevents the practitioner from doing unnecessary treatment.
In summary, lactulose may over-report positive SIBO test results, while glucose may under-report. When we look at the studies, they actually favor the use of the glucose breath test. Both tests have merit. Both tests can be used. The key is to find a skilled practitioner to help you out.
Also, with lactulose, if you only see elevated gas levels at the very end of the test around 100 or 120 minutes, then that could very likely be a false positive.
With glucose, if you see positive SIBO, then that person definitely has SIBO. However, if a person tests negative for SIBO using glucose, but they have symptoms suggesting SIBO, then it could have been missed on the glucose breath test. In this case, you may want to consider a lactulose breath test or consider treating them for SIBO.
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