How to Test for SIBO at Home

How to Test for SIBO at Home

Perhaps you are convinced that your endo belly is actually small intestine bacterial overgrowth, or SIBO, but you don’t know how to go about getting tested. In this column, I’ll show you how to get started.

The main SIBO test is a breath test that measures the amount of gas produced by the bacteria in the small intestine, indicating the presence of SIBO.

There are three types of SIBO: methane, hydrogen, and hydrogen sulfide.

At this stage, the breath tests only check for methane and hydrogen, but in some cases, we may be able to identify the hydrogen sulfide SIBO type if a specific pattern is present in the results (more on that here).

The breath test includes a simple sugar substrate that you swallow before testing. The substrate is either glucose or lactulose, which essentially feeds the SIBO so that bacteria or archaea produce gas.

The test requires you to breathe into 10 test tubes. You would do this once before drinking the substrate so that the lab can measure against a baseline. Then you’d drink the substrate and breathe into nine more tubes every 20 minutes across a three-hour window.

After that, you’ll send the test results back immediately to be analyzed, so make sure to do it on a day when you can get out to mail it.

The test can be a little fiddly, so it helps to watch an instructional video beforehand.

Getting a good test can be tricky. I haven’t had a client yet who has managed to obtain the most accurate test through a doctor who isn’t specialized in SIBO. I prefer clients to order tests privately so they have control over the type of breath test they do.

The first thing to consider when ordering a test is which substrate to choose.

Lactulose travels through the small intestine where SIBO would be; and the large intestine, which naturally houses bacteria, so fermentation is expected. This is helpful for us when looking for the methane type of SIBO (more on that soon). But if the lactulose travels the small intestine more quickly than expected, it might cause a false positive from the fermentation in the large intestine.

Generally, the first two hours of the test is when the substrate is in the small intestine, and the third hour is when the substrate is expected to enter the large intestine. However, given that most people with SIBO have slower gut motility — the main cause of SIBO — the chances of a false positive are lower, as it’s unlikely the lactulose will make its way through the gut too quickly.

Glucose, on the other hand, can give false negatives because it’s readily absorbed and doesn’t make it through the entirety of the small intestine. Instead, it usually only manages to make it through the first 3 feet of the small intestine, which means that if the SIBO is further down, we’ll miss it.

I’ve trained with naturopathic doctor Allison Siebecker, who generally prefers a lactulose test to a glucose one, though she says both tests would be ideal. If a glucose test is negative, a lactulose test is needed to confirm. For that reason, my clients and I stick with lactulose, as long as they’re happy with the choice.

The second thing to watch for is the length of the test. Some tests are only two hours or two and a half hours, because they’ve assumed the substrate would be out of the small intestine within the first two hours. However, we know this isn’t the case. Slow gut motility is a problem for many, so we need that final third hour or the SIBO might be missed entirely.

Does that mean there may be false positives because fermentation in the large intestine is mistaken for small intestine fermentation? Maybe, but most tests have a pattern, which helps us to differentiate the difference between the two.

Normally, there’s a slight dip in gas production as the substrate makes its way into the large intestine. This results in two peaks with a dip in the middle on the graph of results that charts gas production. I have seen multiple test results from Siebecker and with my clients that show this dip happening later in the test. This means that there’s no rise in gas until after the second hour, which if the test had stopped then, would have missed the SIBO gas production entirely.

Essentially, in my experience, the most reliable test would be a three-hour test with 10 test tubes and a lactulose substrate. You can find labs that do this test here.

In later columns I’ll discuss how to prepare for a SIBO test and how to understand your results.


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