Small Intestinal Bacterial Overgrowth (SIBO) is a condition characterized by an excessive growth of bacteria in the small intestine. Diagnosing SIBO accurately is crucial for effective treatment, and one of the primary diagnostic tools is breath testing. Breath tests typically use either lactulose or glucose as substrates.
Breath Testing for SIBO Breath testing measures the amount of hydrogen and methane gasses produced by bacteria in the small intestine. These gasses are not produced in significant quantities by human cells but are byproducts of bacterial metabolism. The presence and levels of these gasses in the breath can indicate bacterial overgrowth.
Types of Breath Tests
- Lactulose Breath Test (LBT)
- Glucose Breath Test (GBT)
Lactulose Breath Test (LBT) Lactulose is a non-absorbable sugar that passes through the small intestine into the colon. When lactulose is fermented by bacteria in the small intestine, it produces hydrogen and methane, which are absorbed into the bloodstream and exhaled in the breath.
Procedure
- Preparation: Patients fast for at least 12 hours before the test.
- Baseline Breath Sample: A baseline breath sample is collected to measure hydrogen and methane levels.
- Ingestion: The patient drinks a lactulose solution.
- Sampling: Breath samples are collected at regular intervals (usually every 15-20 minutes) for about 2-3 hours.
Interpretation There are a variety of published diagnostic criteria for lactulose breath tests. These are the most clinically relevant SIBO diagnostic criteria:
- A rise over lowest preceding value in hydrogen production of 20 parts per million (ppm) or greater within 120 minutes after ingesting lactulose
- A rise over lowest preceding value in methane production of 10 ppm or greater within 120 minutes after ingesting lactulose
- A rise over lowest preceding value in the combined sum of hydrogen and methane production of 15 ppm or greater within 120 minutes after ingesting lactulose.
Advantage
- Can detect overgrowth throughout the entire small intestine.
Disadvantage
- Potential for false positives due to rapid transit time or colonic fermentation are possible, but most experienced practitioners can reduce false positives by combining clinical presentation with the tests results.
Glucose Breath Test (GBT) Glucose is a sugar that is absorbed in the proximal small intestine (the first part of the small intestine). If bacteria are present in this region, they will ferment glucose, producing hydrogen and methane.
Procedure
- Preparation: Similar to the lactulose breath test, patients fast before the test.
- Baseline Breath Sample: A baseline breath sample is collected.
- Ingestion: The patient drinks a glucose solution.
- Sampling: Breath samples are collected at regular intervals for up to 2-3 hours.
Interpretation There are a variety of published diagnostic criteria for glucose breath tests. Below are the most clinically relevant SIBO diagnostic criteria:
- A rise over lowest preceding value in hydrogen production of 12 parts per million (ppm) or greater within 120 minutes after ingesting glucose.
- A rise over lowest preceding value in methane production of 10 ppm or greater within 120 minutes after ingesting glucose.
- A rise over lowest preceding value in the combined sum of hydrogen and methane production of 12 ppm or greater within 120 minutes after ingesting glucose.
Advantages
- Higher published specificity and lower false positive rate compared to lactulose, although this is less of an issue with an experienced practitioner.
- Less likely to be influenced by colonic bacteria since glucose is usually absorbed before reaching the colon.
Disadvantages
- May miss bacterial overgrowth in the distal (farther) parts of the small intestine.
- Does not provide additional information on colonic bacterial activity.
Comparison of Lactulose and Glucose Breath Tests
Lactulose Breath Test
- Pros: Can assess the entire small intestine
- Cons: Higher rate of false positives due to colonic fermentation; influenced by intestinal transit time
Glucose Breath Test
- Pros: Higher specificity; less influenced by colonic bacteria
- Cons: May not detect overgrowth in the distal small intestine
Clinical Considerations Test Selection
- The choice between lactulose and glucose breath tests depends on clinical judgment and specific patient circumstances.
- Some practitioners may prefer one test over the other based on their familiarity and the patient’s symptoms.
Results Interpretation
- Both tests require careful interpretation by experienced clinicians to avoid misdiagnosis.
- False positives and negatives can occur, so results should be considered alongside clinical symptoms and other diagnostic information.
Summary
Breath testing with lactulose and glucose provides a non-invasive and relatively simple method for diagnosing SIBO. Each test has its advantages and limitations, and the choice of test should be tailored to the patient’s needs and clinical presentation. Accurate interpretation of these tests is crucial for effective diagnosis and management of SIBO. for the diagnosis of SIBO are available and have their own pros and cons.
For further detailed information, consult sources such as:
- Pimentel, M., et al. “Hydrogen and Methane-Based Breath Testing in Gastrointestinal Disorders: The North American Consensus.” The American Journal of Gastroenterology.
- Lauritano, E. C., et al. “Small Intestinal Bacterial Overgrowth and Irritable Bowel Syndrome.” Gut.
