SIBO testing can be tricky because it is challenging to get a 100% accurate picture of the bacteria in the small bowel. This is because the small intestine is hard to reach. To see or sample the small intestine a colonoscopy only reaches the end portion of the bowel and an endoscopy only reaches the top part. The small intestine is estimated to be around 20 feet long so there is a large part in the middle that we can’t reach easily.
In this guide, I will walk you through everything you need to know about breath testing and how it can be used to diagnose SIBO. Testing is important because it determines the treatment approach you take based on your gas levels.
The concept of breath testing is pretty simple. We feed bacteria in our gut to see what kinds of gases bacteria produce and where they are being produced. All bacteria ferment carbohydrates. Remember, we are supposed to have smaller amounts of bacteria in our small intestine so breath testing is a good way to tell if we are producing too much gas where it shouldn’t be produced.
To complete a breath test you first eat a sugar substrate (either lactulose or glucose). This sugar substrate then goes into your intestine where bacteria ferment it and produce gases like hydrogen, methane, hydrogen sulfide and carbon dioxide. These gases then travel to the lungs and are exhaled in your breath. The breath test then measures these gases in your breath and the timing in which the gases are produced after ingesting the sugar substrate determines whether these gases are being produced in the colon or the small intestine.
It usually takes about an hour and forty-five minutes for the sugar to reach the colon. This means that your doctor will be looking for spikes in your gas levels before the sugar reaches the colon to determine if you have overgrowth in your small bowel.
Currently, for measuring SIBO we evaluate levels of hydrogen and methane in the breath, but in the future, the technology to detect hydrogen sulfide will be available. This new technology will be important for people who have the third type of gas found with SIBO, hydrogen sulfide.
How Do You Conduct a SIBO Breath Test?
Breath tests can be ordered by your doctor and conducted in the office or you can take the test in the comfort of your own home. The medical company will simply ship the kit which includes your sugar solution and test tubes to your home.
In order to get accurate test results, you MUST follow a specific testing process.
SIBO Test Prep Process:
Order your kit online which is shipped to your house
Follow a low-fermentation diet for 1-2 days prior to test day
Fast for 12 hours the evening before your test in the morning
Test Day Process:
Grab a timer and book to have for the 3 hour testing period
Before drinking lactulose, take a baseline breath sample a few minutes before the hour (7:57)
Drink your dose of lactulose or glucose to start feeding bacteria
Every 20 minutes for the duration of your test breathe into the small test tubes
After taking a breath sample seal each tube and restart your timer
When finished, put your tubes back in the box and mail to lab
It’s important that you follow the breath test preparation guidelines by eating a low-fermentation diet and fasting for 12 hours. If you do not do this it can cause a false test result. The reason doctors instruct you to follow these guidelines is that you want to start the test with a normal baseline of fermentation. If you go into the test eating broccoli and cauliflower that will naturally elevate your gas levels making it difficult to gauge a true overgrowth.
The video below explains the test in more detail:
Difference Between Lactulose and Glucose for SIBO Breath Testing
The two types of sugar substrates used for breath testing are lactulose and glucose. When you ingest lactulose or glucose bacteria feeds on these sugars and produces gases like hydrogen and methane which we are then able to measure in a breath test. But, there are some key differences between both sugar substrates.
So, what’s the difference between the 2 types of sugars used for testing?
Lactulose Tests: Lactulose is a sugar that humans cannot digest, only bacteria can. Lactulose does not get absorbed and reaches the end of the small intestine which is where SIBO is thought to be more common. This allows us to get a picture of the whole small intestine.
Lactulose will diagnose SIBO at the end of the small intestine
Most common sugar used in breath testing
Glucose Tests: Glucose is a sugar that is absorbed by humans and bacteria. Glucose is absorbed higher up in the small intestine (first 3 feet of small bowel) which shows us if SIBO is present in the upper part of the small intestine. Unfortunately, this test does not show us if SIBO is present at the end of the small intestine since it is absorbed so quickly. This is why a lot of doctors use lactulose.
Doesn’t diagnose SIBO at the end of the small intestine
If someone tests positive with glucose we know that they for sure have SIBO higher up in the intestine
The most commonly used SIBO breath test is a 3-hour lactulose test.
There is a benefit if you are willing to do both glucose and lactulose breath tests because you will be able to tell with the glucose test how high up the bacteria are, but you should always do the lactulose test to measure the whole length of the small intestine.
Interpreting SIBO Breath Test Results
Interpreting SIBO breath test results can be tricky. Doctors basically check your levels of hydrogen and methane throughout the 2-hour test and look for elevated levels of hydrogen or methane during the 2-hour small intestine transit time.
It’s important to note that you must test for both hydrogen and methane. This is because methane producing bugs (methanogens) consume hydrogen gas to produce methane. If you just tested for hydrogen you could miss a positive SIBO diagnosis because the test could show low levels of hydrogen when in reality the methane bugs are eating that hydrogen to produce methane gas.
There is also a third gas called hydrogen sulfide which a portion of SIBO patients produce. Currently, we do not have the technology to detect this gas but it can be problematic as well. This is when things can get more complicated, but the hydrogen sulfide producing bugs also consume the other gases to produce h2s. Often times, people with excessive hydrogen sulfide gas will show a flat line graph. Don’t worry, your doctor should be able to interpret this for you!
Below are the typical positive and negative test results.
Typical positive SIBO breath test results:
Hydrogen or methane is >20 ppm up to 120 minutes after ingesting the solution
Hydrogen or methane is elevated at baseline >20 ppm
Negative SIBO breath test results would typically be:
Hydrogen or methane is <20 ppm up to 120 minutes after ingesting solution
Usually, hydrogen or methane stays below 20 ppm up to 120 minutes until it reaches the large intestine spike
In the test graphs below, you can get a picture of what a negative and positive result looks like. The charts on the left-hand side are negative and the charts on the right-hand side are positive.
You must follow a SIBO breath test prep diet for 1-2 days prior and fast for 12 hours before testing
You can do the breath test with a take-home kit and mail it in to be evaluated or take in your doctors office
If your test shows high gas levels this may indicate a longer treatment period to reduce them
You and your doctor need to see the whole breath test graph to interpret it correctly
The breath testing machine must be calibrated and test for methane
Re-testing is very important after doing any SIBO treatment to see how much the gas levels have decreased
Where Can You Get a SIBO Breath Test?
There are now SIBO breath tests that you can order directly to your home without a prescription. Yes, it’s always important to seek the care of a great doctor, but sometimes you need to find out if you’re dealing with SIBO before spending money to see a specialist.