When you’re trying to figure out what’s causing your symptoms, testing is often top of mind. You want answers and a definitive diagnosis of the problem so that you can find the right solution, and testing promises to get you there.
However, there are times when testing can be more of a hindrance than helpful. For the diagnosis of SIBO, or small intestinal bacterial overgrowth, the most common type of test is a SIBO breath test. But what kind of breath test is best, and what do the results mean?
In this article, we’ll discuss the different types of SIBO and the different breath tests. Plus, we’ll cover how they work and what the results mean. We’ll also discuss when it’s necessary to do a breath test before starting treatment.
What Is SIBO?
SIBO, or small intestine bacterial overgrowth, is just what it sounds like: an overgrowth of bacteria in the small intestine where normally there should be hardly any bacteria at all. SIBO can cause a variety of digestive and non-digestive symptoms.
Symptoms of SIBO may include:
- Abdominal pain
- Diarrhea, constipation, or other alterations in motility, leading to the need for laxatives
- Weight loss or nutritional deficiencies resulting from nutrient malabsorption
- Food intolerances/allergies
- Brain fog
- Leaky gut
- Histamine reactions [1, 2]
Types of SIBO
There are three different types of SIBO, classified by the dominant type of gas produced by overgrown intestinal bacteria: hydrogen, methane, or hydrogen sulfide. The hydrogen type is generally associated with fast transit time and diarrhea . The methane type is associated with slow transit time and constipation . The third type, hydrogen sulfide, is still a relatively new discovery and has been associated with diarrhea and abdominal pain .
IBS and SIBO
SIBO has been linked to irritable bowel syndrome (IBS) and may be an underlying cause of symptoms. A systematic review and meta-analysis of SIBO cases in IBS patients indicated that over one-third of IBS patients tested with breath testing were positive for SIBO .
They also showed that methane-positive breath tests were more present in patients with IBS-C (constipation dominant IBS) .
Other Conditions That May Contribute to SIBO
There are many conditions that may contribute to SIBO, including gut-related and autoimmune conditions, and even physical injury. Some of these conditions are:
- Celiac disease 
- Inflammatory bowel disease (Crohn’s disease and ulcerative colitis) 
- Fibromyalgia 
- Chronic constipation [10, 11]
- Abdominal adhesions (common after abdominal surgery) 
- Metabolic dysfunction (being overweight, or having high blood sugar or high cholesterol) [12, 13]
- Hypothyroidism 
Chronic use of certain medications like proton pump inhibitors (PPIs) may also increase the risk of developing SIBO .
SIBO Breath Test Overview
A functional medicine practitioner may use a breath test, along with symptom presentation, to determine whether a patient has SIBO. There are two main types of breath tests: the lactulose breath test and the glucose breath test.
Depending on the test, the patient will drink either a lactulose or a glucose sugar solution to stimulate the gut bacteria to produce gas.
This is where understanding the tests may get confusing, so we’ll break it down further.
Hydrogen, methane, and now hydrogen sulfide are the three types of gases that can be measured with a SIBO breath test. These gases are what we test for, while lactulose and glucose refer to how we test.
Let’s look at the differences between the solutions used (lactulose and glucose) as well as the different gases the breath test looks for (hydrogen, methane, and hydrogen sulfide).
How It Works
For each type of at-home test kit, you drink either a lactulose or glucose sugar solution, and then collect breath samples by exhaling into a series of sealable bags over 15 or 20-minute intervals. The breath samples are then sent to the lab where a technician will evaluate levels of gases produced by gut bacteria.
Until recently, breath tests were only able to measure the amount of hydrogen and methane gas being produced. But after identifying a third type of SIBO, called hydrogen sulfide SIBO, researchers developed a new test called the trio-smart. This test still uses a lactulose or glucose solution, but technicians are now able to look for all three gases for a more complete picture of an individual’s small intestinal bacterial community.
Which SIBO Breath Test Is Best: Lactulose or Glucose?
Lactulose and glucose breath tests have been compared extensively. In the meta-analysis review, “Breath Test for Non-Invasive Small Intestinal Bacterial Overgrowth Diagnosis: A Systematic Review with Meta-Analysis,” researchers found that glucose tests are more reliable in their sensitivity and specificity . This means that glucose testing more often correctly diagnoses those who have SIBO and correctly identifies those who do not have SIBO.
- Sensitivity tells you if you were correctly diagnosed with the condition.
- Specificity tells you if you were correctly found not to have that condition.
In the study, glucose breath tests showed a sensitivity of 58% and a specificity of 83%, compared to 42% sensitivity and 70% specificity for lactulose breath tests .
What do these numbers mean? Lower numbers indicate a higher likelihood of false negatives or false positives.
This data clearly indicates that the glucose breath test has better scores for both sensitivity and specificity. In other words, glucose breath tests are better able to both correctly diagnose those who have the condition and correctly identify those who do not.
Lactulose breath tests can still be helpful when interpreted by a practitioner who understands the importance of timing and the risk of false positives, but it’s hard to know how often this is really the case. Unfortunately, since this is still the most commonly used SIBO breath test, false positives may be quite prevalent.
It is important to have reliable testing since SIBO patients may have to undergo significant dietary changes and microbial treatment protocols that could be unnecessary and potentially harmful for someone who does not have SIBO.
This doesn’t mean a lactulose test is always invalid, especially when used by an experienced clinician in combination with symptom presentation and patient history. However, glucose breath testing is ideal.
Lactulose Breath Test Drawbacks
Research has shown that lactulose testing tends to be less reliable and easier to misread .
Why is this? The misreading occurs in the timing of the test. This is a common error that can lead to incorrect diagnosis of small intestinal bacterial overgrowths.
Let’s break that down a bit further. Research indicates that the preferred window for reading gas levels is between 80 and 90 minutes after lactulose or glucose ingestion, but you could go up as high as 100 minutes . The 80- to 90-minute mark is important because it shows the transition from the small to the large intestine.
Here is what a typical SIBO breath test result looks like:
You can see that in this example, the gas reaches high levels at around the 80-minute mark. It increases slightly between 80 and 100 minutes, and then slowly declines.
The problem is that lactulose testing may not show elevated gas levels until after the 100 minute mark, when the gas would be present in the large intestine instead of the small. Someone with elevated gas after this point should not necessarily be diagnosed with SIBO, since gas in the large intestine is normal.
It’s important to understand these nuances in the test timing in order to correctly diagnose or rule out SIBO. Otherwise, those who have a gas elevation at 100 or 120 minutes, and sometimes even at 140 minutes, may be told they have SIBO when they don’t. They may then be prescribed antibiotics and other treatments that can be costly and that aren’t actually necessary.
Glucose Breath Test Advantages
Fortunately, the glucose breath test seems to protect against the false positive issue. A meta-analysis from 2020 showed that glucose breath tests were more reliable than lactulose breath tests for correctly diagnosing SIBO .
The advantages of glucose tests are:
- Higher sensitivity and specificity rates, indicating greater accuracy.
- Glucose is absorbed rapidly in the small intestine, whereas lactulose is not broken down until it reaches the colon. This makes glucose a more reliable medium to look for gas production in the small intestine .
However, as with the lactulose breath test, there is still opportunity for misdiagnosis using the glucose breath test. It’s always important to look at test results as one part of a complete picture of your health .
Testing for the Different Gases
Now that we know how we test, let’s look at what we’re testing for. Remember our distinction earlier that the methods (either glucose or lactulose testing) are used to measure levels of various gases (hydrogen, methane, or hydrogen sulfide) produced by overgrown bacteria.
Hydrogen vs. Methane SIBO
We now have the ability to test for a third type: hydrogen sulfide SIBO .
Hydrogen Sulfide SIBO and Trio-Smart
Hydrogen sulfide SIBO may cause diarrhea and abdominal pain, inflammation, immune system overreaction, cytotoxicity, sulfur-smelling gas and belching, indigestion, heartburn, and more.
Practitioners were not previously able to order a breath test to look for hydrogen sulfide SIBO because such a test did not exist — until now.
In 2020, researchers introduced the trio-smart breath test. This test identifies hydrogen, methane, and hydrogen sulfide SIBO types. This means that you can get a complete picture of the gas profile in your small intestine.
If you’re someone who suspects or has what has now been identified as hydrogen sulfide SIBO, that means you may receive a false negative on a standard SIBO breath test. False negatives are likely in this case because those tests can’t identify this type of gas. Now there is a test available for you to get a more complete picture of your SIBO.
This information is invaluable in determining appropriate treatment for SIBO patients, as treatment depends on their specific SIBO profile. Patients can save time, money, and the stress of additional testing by doing one test that gives them a full picture of the gases present.
Do You Really Need a Breath Test to Diagnose SIBO?
Breath tests can provide an important piece of the picture, but symptom evaluation and accurate patient history are just as valuable when it comes to diagnosing SIBO.
If you and your clinician suspect you have SIBO, but you can’t afford or don’t wish to pursue diagnostic tests, there are therapeutic options you can start right away, including probiotics and diet modification, among others [18, 19].
Many people get stuck on the idea of testing, but often it’s best to dive straight into practices that actually improve gut health, relieve some symptoms, and then come back to testing later if needed. The goal is to get you feeling better as quickly as possible.
Consult a Functional Medicine Practitioner to Get Help with SIBO
If you’ve been struggling with the symptoms of SIBO and are ready to figure out what the root cause really is, reach out to us and book an in-person or virtual consultation. Our team has decades of combined experience in treating complex gastrointestinal illnesses and symptoms. Become a patient today.