Testing For SIBO (Small Intestinal Bacterial Overgrowth)





If you read my last blog post, Is SIBO or SIFO (Small Intestinal Bacterial/Fungal Overgrowth) Causing Your IBS? and this resonated with you, keep reading. This blog post is all about how to test for SIBO, using the Lactulose Breath Test.


We know that SIBO is massively underdiagnosed and could be responsible for up to 85% of IBS cases. But why is SIBO so commonly missed or overlooked?

A big part of the problem is lack of knowledge and testing availability for SIBO in the medical community.

Many people assume they need to go to their doctor for this test, only to find out their doctor is unfamiliar with it. In many countries, you can actually order this test straight from the internet, as it's an 'at-home' test. Although I definitely encourage you to work with someone who has experience in interpreting lactulose breath test results and providing the appropriate treatment protocol, my point is, this doesn't necessarily need to be a medical doctor.


In this blog post, we will cover:


- The lactulose breath test

- Limitations of the test

- Do you have to test?

- Hydrogen Sulfide SIBO

- What about stool tests?



The Lactulose Breath Test


The ‘gold standard’ for non-invasive SIBO testing is a breath test that measures the levels of hydrogen and methane gas in your breath. I use the SIBO Lactulose Test with my clients, which is a simple, non-invasive test that can be ordered online and completed at home.

After a 1-2 day prep diet, a baseline breath sample is taken before a lactulose solution is swallowed and breath samples are collected every 15-20 minutes for 2.5 to 3 hours (depending on the lab used), so 10 samples in total. If bacteria are present, they will ferment the lactulose and produce hydrogen and/or methane gas, which we can then measure through your breath.

In simple terms, if the gas levels are above a certain number within a certain time period, then the test indicates a positive result for SIBO. Using the correct solution and interpretation of results is a science all and of itself. Having a practitioner, skilled in the interpretation of SIBO breath tests is key to getting the right diagnosis. See below for a sample of what test results look like.




Interpreting the results


Interpretation is not always black and white, but here are a few different measurements (but not all) we are looking for that may indicate the presence of SIBO:


Lactulose Test:

  • Rise of 20ppm in hydrogen above baseline within 90-120 minutes - Hydrogen Dominant SIBO.

  • Rise of 12ppm in methane above baseline within 90-120 minutes - Methane Dominant SIBO

  • Combined rise in hydrogen and methane of 15ppm above baseline within 90-120 minutes - Mixed SIBO.

  • Elevated baseline methane level that remains high (above 12ppm) - Methane Dominant LIBO (Large Intestine Bacterial Overgrowth) or potential H.pylori infection.

  • Flat-lining (below 3-4) of both hydrogen and methane gas for the entire duration of the test period - Suggestive of Hydrogen Sulfide SIBO.



Limitations of the test


Like many tests, the Lactulose Breath Test does have limitations that need to be considered.

One problem I personally come across with this test is when clients do not following the prep instructions closely enough, or not taking the samples correctly, resulting in an invalid test result.

This can be frustrating, considering the test takes 3 hours to complete! But, most people don't have this problem if they watch the instructional video provided prior to taking the samples, and allow enough time to prep.

Another limitation to consider is the risk of a false positive test result with the lactulose breath test. The lactulose breath test is generally favoured within the SIBO practitioner community and is the substrate solution I most commonly use with clients. The reason we use lactulose is that it is scientifically proven to travel through the full length of the small intestine to the distal portion where SIBO typically likes to hide; i.e. close to the large intestine. Glucose is an alternative substrate used, but there is limited research at this time about whether glucose has the same ability to reach the distal part of the small intestine.

However, numerous studies have shown the ability for lactulose breath tests to be interpreted incorrectly and clients given false positive results. That is, they are told they have SIBO when they really don’t. How does this happen? It’s all do with transit time; how fast the lactulose moves through your small intestine and into your large intestine.

As we have previously discussed, while a huge amount of bacteria live in the large intestine, SIBO occurs when bacteria move to where they don’t belong and colonise the small intestine, a region that should contain very limited numbers of bacteria. So ideally, gas levels in the small intestine will be low, while they will be higher in the large intestine where all the bacteria live and feed on the lactulose solution. The breath test assumes that the lactulose solution that you drink will not make it’s way through to the large intestine in the first 90 minutes of the testing period.

But, for those with an anatomically shorter intestine or faster transit time (often those with diarrhea-dominant symptoms), if the lactulose makes its way through the small intestine faster than expected, then you’ll likely get a false elevation of gas. When looked at in isolation and without a full history of symptoms and other variables, a practitioner might diagnose you with SIBO, when in fact, the elevated gas levels are coming from the large intestine, rather than the small intestine.


This is one of the reasons why there is a lot of fear surrounding SIBO treatment. Lots of people have heard or read that you can never get rid of it; of people repeatedly treating it, retesting and still showing (false?) positive test results. And while for a small subset of people, just gaining symptomatic relief can be a long process, for the majority of clients SIBO is something that can be overcome. But if you don’t understand how to 1) treat SIBO and 2) interpret test results, you can fall into the trap of believing you’ll never be able to get rid of it!

The concept of false positives is really important for you to understand so that you don’t feel like there is something wrong with you or that you have failed somehow in taking the antimicrobials or eating something you shouldn’t have. It also means that if you’ve improved symptomatically, then there might be no need to continuously be treating something that doesn’t actually exist, but is an error with interpreting your test results.



Do you have to test?


This is a question I get asked a lot, and my answer may be a little different from a lot of other practitioners. In an ideal world, everyone would test, and then retest after treatment. But I understand that is isn't always possible for everyone. It may not be possible financially. Many people have to make a decision between investing in help with treatment advice and investing in testing. If this is you, I always recommend investing in help with treatment over testing. The reason is, as you hopefully now understand, you need someone experienced in SIBO to interpret your results. So if you have invested all your money in testing, but are unable to now enlist help to interpret those results and provide accurate treatment recommendations. You are essentially left to Google and trying to work out the answers yourself.

In my experience, if you're on a tight budget, it's better to invest in help. An experienced practitioner should be able to provide you with a sound treatment plan based on your health history and symptoms, and then playing close attention to how you respond to the plan. This method takes a little more trial and error, but it's a lot better than trying to navigate your own healing journey based on your test results. I much prefer it when my clients can invest in all the testing, because it makes my life easier, and provides a lot of peace of mind. But, I have successfully treated many clients without testing and just going on the assumption they have SIBO based on their symptoms and how quickly they respond to treatment. The bottom line is - don't let it stop you from starting the healing process and seeking help.


Hydrogen Sulfide SIBO


Hydrogen sulfide SIBO is the less commonly understood type of SIBO, which there is currently no breath test available for detecting it, making it difficult to diagnose. However, flat lining of methane and hydrogen on a lactulose breath test (below 3-4 for the duration of the test), when symptoms of smelly rotten-egg gas are present, can indicate the presence of hydrogen sulfide SIBO and should be treated accordingly.


What about stool tests?


Stool testing is another method for testing for dysfunction and imbalances in the gut, and many people wonder if this is an accurate way to test for SIBO. Although stool testing has made many advances in recent years and is a very useful tool when it comes to understanding our digestive issues, it does not detect SIBO. This is simply because a stool test is looking at more what is going on in the large intestine. There are some useful markers that may correlate with SIBO, but this is not a cost effective or reliable test for SIBO.


Final thoughts...


SIBO lactulose breath testing is a very useful diagnostic tool, and definitely something you should consider if you have IBS, or daily issues with bloating, gas, and other SIBO related symptoms discussed.

To have the test completed with me, you need to be completing my program The IBS Protocol (enrollment opens soon!!), or be working with me 1:1. If you're interested in getting this process started, book a FREE 20 minute discovery call with me. These are no obligation chats, where you can ask any questions you may have before committing.


Talk soon,


Chrystie x




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