From the Guidelines
Interpreting a hydrogen and methane breath test for SIBO requires understanding the specific gas patterns over time, with a positive test typically showing hydrogen levels rising by ≥20 ppm or methane levels by ≥10 ppm above baseline within 90 minutes after consuming the test substrate, as supported by recent work in the UK and USA to develop evidence-based consensus guidelines for breath testing 1. To accurately interpret the results, it's essential to establish baseline readings before the test and follow pre-test protocols, including dietary restrictions, fasting, and avoiding antibiotics prior to the test.
- Key factors to consider when interpreting the test results include:
- Early gas peaks, which indicate bacteria in the small intestine fermenting the sugar before it reaches the colon
- Baseline readings, which should be established before the test
- Pre-test protocols, including dietary restrictions (avoiding high-fiber foods 24 hours before), fasting for 12 hours, and avoiding antibiotics for 2-4 weeks prior
- False positives and false negatives can occur due to various factors, such as rapid transit time or recent antibiotic use, and should be taken into account when interpreting the results. The breath test works because intestinal bacteria produce hydrogen and methane when fermenting carbohydrates, which are then absorbed into the bloodstream and expelled through the lungs where they can be measured, as described in the context of orocaecal transit measurement using the rise in breath hydrogen due to the degradation of ingested polysaccharides 1. A positive test result should be followed by treatment, which may involve antibiotics like rifaximin, and addressing underlying causes to prevent recurrence, with the goal of improving morbidity, mortality, and quality of life outcomes.
From the Research
Interpreting Hydrogen and Methane Breath Test Results
To interpret the results of a hydrogen and methane breath test for small intestine bacterial overgrowth (SIBO), it is essential to understand the criteria for a positive test.
- A positive breath test is defined as fasting hydrogen ≥ 20 ppm or fasting methane ≥ 10 ppm, or a rise of ≥ 12 ppm hydrogen or ≥ 6 ppm methane over baseline during the test 2.
- The test measures the amount of hydrogen and methane in the breath, which are produced when bacteria in the small intestine ferment carbohydrates 3.
- The North American Consensus guidelines recommend the following cut-off values for SIBO diagnosis: a rise in hydrogen of ≥ 20 ppm by 90 min during glucose or lactulose breath test, and methane levels ≥ 10 ppm 4.
Factors Influencing Test Results
Several factors can influence the results of a hydrogen and methane breath test, including:
- The dose of substrate used for the test: 10 g lactulose may produce fewer positive SIBO results than 16 g lactulose, while 75 g glucose may produce more positive results than 50 g glucose 5.
- The duration of the test: performing carbohydrate malabsorption breath tests for 180 min may increase the number of positive results compared to 120 min 5.
- The presence of methane-producing bacteria: some patients may produce methane instead of hydrogen, and a simple hydrogen breath test may not detect these cases 6.
Clinical Applications
Hydrogen and methane breath testing has several clinical applications, including:
- Diagnosing SIBO: the test can help identify patients with SIBO, which is characterized by an overgrowth of bacteria in the small intestine 2, 3.
- Evaluating carbohydrate malabsorption: the test can help diagnose malabsorption of carbohydrates such as lactose, fructose, and glucose 4.
- Assessing bloating and gas: the test can help evaluate patients with bloating and gas, which can be symptoms of SIBO or carbohydrate malabsorption 4.