SIBO Tests

A SIBO diagnosis can be made by 2 non-invasive tests: SIBO Breath Test and IBS Blood Test. Both are available as at-home tests. A third option is endoscopy with culture, which is primarily used in research. The SIBO breath test shows the gas type and severity, which is important for choosing treatment type and length (number of treatment rounds), thus the SIBO breath test is the clinical standard. Breath tests can be used to diagnose several conditions: H pylori infection (Urea Breath test which tests CO2), carbohydrate malabsorption (i.e. lactose malabsorption), and SIBO.
Affiliate links include: True Health, Rupa, Direct labs, FoodMarble and Amazon. 

​​1. SIBO Breath Test Overview
​& Interpretation 

SIBO breath testing measures the hydrogen, methane and/or hydrogen sulfide gas produced by bacteria in the intestines (via fermentation), that has diffused into the blood, then lungs, for expiration in the breath. Hydrogen and methane are gases produced by bacteria/archaea, but not by humans, thus these gases indicate the presence of bacteria in the intestines. Hydrogen sulfide gas is made by both humans and bacteria - the amount of gas indicates overgrowth based on positive criteria.

How It's Performed: Patients drink a sugar solution (substrate) of lactulose, glucose or fructose after a 1 day preparatory diet, and baseline breath sample before the test begins. The prep diet removes much of the food that would feed the bacteria (plant foods), allowing for a clear bacterial reaction to the substrate. Breath is collected every 15-20 minutes over 2 or 3 hours. Despite the fact that the test encourages bacteria to make gas (which can lead to symptoms), it's usually well tolerated. (see symptom relief options) 
​
Substrate Types: 10 g Lactulose, 75 g Glucose or 25 g Fructose
  • I prefer Lactulose (or Fructose) and don't use Glucose due to high false negative rates - it commonly misses SIBO in those who truly have it. [1]

Where It's Done: At home with either a hand-held device or a kit that is mailed back to the lab, or at a facility with a testing machine (clinic, lab, hospital).

Positive Interpretation: 
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​How To Order a SIBO Breath Test Directly

See the breath test directory below for an international list of labs for practitioner ordering. 

​In the U.S. lactulose is a prescription, which limits its availability. However, several U.S. labs offer direct patient ordering (or for practitioners without prescribing rights). These are 8-9 sample tests: 
  • True Health (all U.S. states, Canada, Europe)
  • Direct Labs (U.S. [excluding NY, NJ, RI] Canada, Europe)
  • Rupa Heath: Genova (U.S. excluding NY, NJ, RI)
  • Trio-Smart (all U.S. states) 
    - This is the only     test that measures hydrogen sulfide
    - Sample breath every 22 min (vs 15 min) to stretch this 2-hour test to my recommended 3 hours - the lab automatically adjusts the graph
Other Options:
The following labs can be ordered with glucose (or no substrate) and then be used with either a separate lactulose prescription, or 25 g fructose. How to get Lactulose and Fructose substrates:
  • Lactulose is a prescription in the U.S. However, many prescribers are willing to order it since it's used as a laxative in higher dose. 
     - ​The prescription is written as: 10g/15mL lactulose #4 oz. Take 10 g/15ml/.35 oz in 8oz water for each test. 
  • Fructose powder is sold at Amazon or grocery stores.
Practitioners interested in running in-office tests with their own machine, can contact ​test manufacturer Quin Tron.

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​Types of SIBO Breath Tests

SIBO tests are differentiated by the gases that are measured, length of test and substrates used. ​The type of SIBO test matters for the best result, however, experts disagree on what makes the best test.
 
Gases measured
Almost all tests measure hydrogen and methane. Some rural hospitals may have older machines that don't measure methane (or simply may not report it). Direct hydrogen sulfide testing is currently only available from one U.S. lab (Trio-Smart). However some cases of hydrogen sulfide can be detected by a flat-line pattern on a 3-hour lactulose test.

Length of test
Different labs offer different lengths of tests, from 1-3 hours. In general the first 2 hours represents the small intestine and the third hour represents the large intestine, though individual transit times vary. A 2-hour test is sufficient for assessing hydrogen overgrowth in the small intestine. But since methane and hydrogen sulfide can overgrow in the large intestine too, 3 hours (with lactulose) is needed for full assessment of these gases, which is why I recommend 3-hour SIBO testing.  

Substrates used
​Lactulose SIBO tests are the first choice for many, because they have a low rate of false negatives, meaning they won’t miss SIBO in someone who really has it. This is because lactulose can indicate overgrowth anywhere in the intestines. It is a lab-made sugar that is not digested or absorbed by humans and does not raise blood sugar. It travels through the intestines intact, making it available for bacteria to ferment in both the small and large intestines. This allows for detection of both small and large intestine overgrowth (methane and hydrogen sulfide can overgrow in either location).   

In contrast, glucose is absorbed into the body within the first few feet of small intestine, making it unavailable for bacteria to ferment into gases after that point, and unable to detect overgrowth in the rest of the small intestine (15+ feet) or large intestine. Thus, a glucose test can miss SIBO in someone who actually has it (false negatives can be high).[1] This means that a negative glucose test is not conclusive. 
 
For this reason, if a glucose breath test is negative, a follow-up lactulose test is then needed to test for SIBO in the rest of the small intestine, and to assess for methane and/or hydrogen sulfide in the large intestine (with a 3-hour test). Additionally, a negative glucose re-test after SIBO treatment, is also not conclusive, because SIBO in the middle and lower small intestine may still be present after SIBO treatment, even if the upper small intestine has been cleared. Thus, retesting with lactulose is advised after SIBO treatment. 
 
The disadvantage of lactulose is the potential for false positives (diagnosing SIBO in someone who doesn't have it), by mistaking a rise of hydrogen in the large intestine for SIBO, if there is fast small intestine transit/motility. The advantage of glucose is a low false positive rate - when it finds it, it's truly there. 

A fructose SIBO test is less commonly used [2] but may be beneficial for detecting overgrowth of bacteria that don't ferment lactulose, and is presumed to test the full small intestine. This is especially helpful for those testing negative on a lactulose test when SIBO is still strongly suspected. Most labs don't offer fructose tests for SIBO, however, a glucose or lactulose test kit can be used with 25 g Fructose. Note that a "Fructose Malabsorption" test is not the same as a SIBO test - it doesn't have enough sample tubes/bags. For more on fructose SIBO testing see Dr. Hawrelak's class in my Free SIBO Resources.

​Which SIBO Breath Test is Best?

Physicians and studies use both glucose and lactulose (and sometimes fructose [2]). I use and recommend the 3-hour, 10-tube, lactulose breath test. Using lactulose over 3 hours allows us to assess overgrowth in the small intestine (first 2 hours) as well as methane and hydrogen sulfide overgrowth in the large intestine (3rd hour) where they can also overgrow. I have found this test to be reliable, accurate, and indispensable in achieving successful patient outcomes. 

Fructose may also be used when lactulose isn't obtainable, or when a negative lactulose test is suspected of being a false negative. 

​Is the SIBO Breath Test Accurate?

A 2010 review of 11 breath testing studies, most commonly using lactulose, found that breath testing in IBS is valid, with a specificity of 83.6%.[3]

However historically, research has shown a lower sensitivity and specificity (accuracy), when breath tests, especially lactulose, were compared to endoscopy with culture, which is considered the gold standard test. Then in 2020, research was able to validate the accuracy of the lactulose breath test against culture testing, by using improved endoscopy collection techniques.[4] [5]

This suggests the problem was the inaccuracy of the culture test that the breath test was compared against. Once the accuracy of the culture test was improved, the statistics lined up, solving the discrepancy. However, many practitioners are not aware of either the 2010 or 2020 findings, while others are waiting for 2020 duplication studies, so confusion over accuracy remains. I personally find the lactulose breath test reliable and accurate.

SIBO Testing Mistakes 

Glucose tests often miss SIBO SIBO tests can miss Hydrogen Sulfide SIBO (ISO)  
  • ​ Trio-Smart is the only direct test for hydrogen sulfide gas 
  • what seems like a tough case, may be undiagnosed hydrogen sulfide
​2-hour tests can miss IMO and ISO (methane and hydrogen sulfide) 
  • use a 3-hour test
  • with Trio-Smart (a 2-hour test): sample every 22 minutes to stretch it to 3 hours
Interpretation is different for each gas, with many nuances
  • 90 minute interpretation for hydrogen can miss SIBO: use 120 minutes
  • the most common methane pattern is a high baseline that stays high
  • 10 ppm methane can miss SIBO: use 3-9 ppm when constipation is present (Dr. Pimentel, myself and colleagues have used this criteria for over 10 years)
Stop laxatives 5 days before testing
  • to avoid false negatives, especially for methane
  • avoid anything that is needed to produce daily BM's, even if they are not "laxatives" (i.e. coffee, fiber, magnesium) 
Testing with GLP-1/GIP medicines (ozempic, mounjaro...) and Gastroparesis can miss SIBO
  • GLP-1 meds may need to be stopped for 1-2 weeks+ for an accurate SIBO test
  • for Gastroparesis - extend test 3-hours past gastric emptying time
While uncommon, SIBO tests may aggravate symptoms temporarily

​2. IBS Blood Test

SIBO underlying cause test and screening SIBO/IBS test.
​The IBS Blood test measures antibodies against the bacterial toxin Cytolethal Distending Toxin B (CdtB) and the small intestine nerve protein Vinculin. It detects SIBO that develops after bacterial food poisoning through an autoimmune process. Food poisoning (also called traveler's diarrhea and stomach flu), is one of the most common causes of SIBO and IBS.
 
Dr. Pimentel (lead SIBO researcher) developed two versions of this test, IBSchek and its 2nd generation updated version, IBS-Smart. Other labs offer versions now as well (see IBS Blood Test Directory box). The test is validated for the diarrhea and mixed type of SIBO/IBS, [6, 7, 8] which is more commonly caused by food poisoning versus the constipation type. However food poisoning can also cause constipation type SIBO/IBS, just less often, with a prevalence of 26.7%.[8] Many of my constipation patients test positive on this test, showing food poising was a contributing cause of their SIBO. SIBO caused by food poisoning is also known as post-infectious IBS (explained here). 
 
The IBS blood test does not replace a SIBO breath test because it doesn't diagnose SIBO from the many other causes besides food poisoning, or show the gas type and severity, which is needed to choose the correct treatment. Whether this test is positive or negative, a breath test is recommended after an IBS blood test. 

​IBS Blood Test: Interpretation and Uses

Interpretation
  • If either antibody is positive, the test is positive.
As a screening blood test for SIBO/IBS
  • If positive, it diagnoses SIBO/IBS from food poisoning, one of the most common causes of SIBO and IBS. A follow up SIBO breath test is then needed to find gas type and severity.
  • If positive, it rules out Inflammatory Bowel Disease (IBD) with 98% probability (with IBS-Smart test).[9] ​
  • If negative, SIBO and/or IBS can still be present from another cause besides food poisoning. A SIBO breath test is then needed to check for SIBO from other causes.
As an underlying cause test
  • If positive, bacterial Food Poisoning is a cause of the SIBO/IBS
  • If positive, deficient migrating motor complex (motility) in the small intestine is the physiologic underlying cause of SIBO (i.e. what went wrong within the body that allowed SIBO to occur). 
An Indicator for Prognosis & Treatment
  • If positive, SIBO is expected to be chronic, and prokinetics are indicated to help deficient migrating motor complex, because there is currently no cure for SIBO/IBS caused by food poisoning. 
  • If vinculin is positive, autoimmunity is indicated, making SIBO harder to treat.

You Tube: Dr. Ali Rezaie discusses IBS-Smart with Dr. Siebecker (beginning of video)

Order your own
​SIBO Breath Test

Lactulose SIBO tests can be ordered directly (without a doctor or prescription in the U.S.) from:  

SIBO Breath Test
​Directory

Disclaimer: The below labs are not recommendations nor is the list complete.  The list is simply provided for convenience. 
UNITED STATES
3-hour, 10-tube tests: (my preference) Hand-held at home device: 3-hour, 8-tube tests:   2:15-hour tests:   2-hour test:
  • Trio-Smart with hydrogen sulfide testing (sample every 22 min vs. 15, to stretch this 2-hour test to my recommended 3-hours - the lab automatically adjusts the graph)
UNITED KINGDOM
GERMANY
AUSTRALIA
NEW ZEALAND
WORLD-WIDE

IBS Blood Test
​Directory

1. IBS-Smart - Gemelli Biotech
(2nd generation with greater specificity)

2. Candida + IBS Profile - Vibrant America

3. Array 22 - Irritable Bowel/SIBO Screen - Cyrex

   Learn more
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