Why your SIBO breath test result may not be reliable

Recently, Small Intestinal Bacterial Overgrowth (SIBO) has been getting more attention in the field of digestive health. It’s been suggested that around 70% of people with Irritable Bowel Syndrome (IBS) might actually be dealing with SIBO. As tests for SIBO become better and more available, more people with SIBO are being identified and are looking for accurate information, support, and effective treatment.

However, there are cases where people who have all the symptoms of SIBO and can’t find any other reason for their stomach issues get a negative result on their SIBO test. Surprisingly, I went through this myself – my first SIBO test came back negative! It was only when another gut specialist reviewed the results that they realized it was a mistake.

Mistakes can happen, and that’s why I want to share more about SIBO breath tests. I want to help you understand them better, read the results correctly, and know why sometimes the test might not be trustworthy. My goal is to save you the time I lost, so you can start your healing journey and get back to feeling your best.

How the Breath Test Works

SIBO breath tests play a pivotal role in diagnosing and understanding Small Intestinal Bacterial Overgrowth (SIBO). During a SIBO breath test, patients drink a sugar solution that feeds bad bacteria in the small intestine. 

If SIBO is present, the bacteria in the small intestine ferment the solution, releasing gasses like hydrogen, methane, or hydrogen sulfide. These gasses are absorbed into the bloodstream and eventually exhaled. 

By measuring these gasses in your breath, it’s possible to determine if you have bacterial overgrowth. Getting the correct diagnosis is an essential tool in tailoring your treatment to you!

Why Test Interpretation Can Be Unreliable

Currently, there’s a gap in medical knowledge about SIBO. Most practitioners aren’t taught in med school how to correctly interpret a SIBO breath test, and often practices vary–meaning that one practitioner may give you a negative result while another may give you a positive one. That’s why I’m so excited about SIBO specialist and educator Dr. Allison Siebecker’s SIBO Pro Course— the only AAFP-certified, ACCME accredited SIBO course that teaches practitioners how to become SIBO specialists.

Along with incorrect interpretation, it’s also possible that external circumstances lead a test to be inaccurate. 

Reasons Your SIBO Test Result May Be Inaccurate

The air in the tubes was drawn from the air and not your lungs. 

If you aren’t breathing properly into the tubes while taking a SIBO breath test, it’s possible that the test could be reporting on air from the room instead of your lungs. This can cause a frustrating false negative even when gas is present in your breath!

Your doctor only looked at the change in gas levels instead of the gas level itself. 

If your breath starts with a certain level of hydrogen and ends with a level not much higher, you may receive a negative result. However, if your level is hydrogen is way too high to begin with, many SIBO specialists will actually see this as a positive result. Depending on how your practitioner reads the test, their interpretation may be inaccurate. 

You should be using another sugar solution. 

Lactulose helps tests the majority of the small intestine, but not all bacteria eat Lactulose. Glucose is a good option, but it only tests the upper part of the small intestine. Fructose is yet another option for a sugar solution that practitioners may use. Sometimes, you’ve simply taken the wrong sugar solution for the bacteria in your small intestine. For the most accurate results, you may want to test using all three. 

The machine isn’t calibrated, or it can’t tell if the air is really from your lungs. 

If the machine isn’t calibrated regularly or it doesn’t measure carbon dioxide in the breath to determine whether samples are valid, you may have received an inaccurate result. Again, this is completely out of your control– but can be a reason your breath test is giving a false negative.

You didn’t follow the prep diet– or you weren’t informed or misinformed about what to eat.

Certain foods and supplements can influence the accuracy of a SIBO test. A good SIBO practitioner will inform you about the correct diet before you begin a SIBO test to make sure your results are as accurate as possible. 

You just finished a course of antibiotics. 

Whether it was for a UTI, sinus infection, or whatever else completely unrelated to SIBO, antibiotics greatly affect gut health and could temporarily have diminished the amount of the bacteria in your small intestine. If you do a SIBO test right after finishing antibiotics or while on a course, your results are most likely a false negative. 

You react to lactulose differently than most people– and you don’t really have SIBO. 

In certain people, lactulose moves too quickly through the small intestine into the large intestine during testing, where bacteria that are normal for the large intestine begin eating and fermenting the sugars. This may show up as elevated gas levels and cause a positive SIBO diagnosis even in a healthy individual. A good alternative for this is using glucose, but as glucose moves slowly through the small intestine, it may not test the bottom half. Again, completely another test with a different sugar solution may be a good option for you if you have suspicions about your SIBO breath test result. 

Although there are many things to consider when it comes to SIBO breath testing, if you work with an educated practitioner or a SIBO specialist the SIBO breath test can be used correctly and present an accurate SIBO diagnosis. If you have been tested in the past but suspect you do (or don’t!) have SIBO contrary to your results, perhaps look into taking another SIBO test keeping these guidelines in mind. 

Hey- have you asked yourself these questions: do I have SIBO? Why, when, and how should I get tested? What’s the dealing with retesting? Our Ultimate Guide to Testing for SIBO will help you gain clarity around this important topic to navigate the maze of SIBO/IMO testing and create an action plan to resolve your symptoms. 


Testing is the first step to seeing recovery and results. You’ll learn the importance of testing and how it can guide your treatment, the 3 ways to be tested for SIBO, what a breath test is, how to choose the right test, do and donts for testing mornings, and how to interpret your results. Get the guide now!

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