From the Guidelines
The lactulose breath test is used to diagnose small intestinal bacterial overgrowth (SIBO) or to measure intestinal transit time, and for this test, you would need to drink a solution containing lactulose, which is a synthetic sugar that humans cannot digest but gut bacteria can ferment, producing hydrogen and/or methane gases. This test is based on the principle that lactulose remains undigested until it reaches bacteria in the intestines; if excessive bacteria are present in the small intestine (SIBO), gas production will occur earlier than expected 1. The amount of lactulose typically given is 10-25 grams dissolved in water. During the test, you would provide breath samples at regular intervals (typically every 15-30 minutes for 2-3 hours) after consuming the lactulose solution. Preparation for this test usually involves following a restricted diet the day before (avoiding high-fiber foods and certain carbohydrates), fasting for 8-12 hours before the test, and avoiding antibiotics for 2-4 weeks prior to ensure accurate results. Some key points to consider when interpreting the results of the lactulose breath test include:
- The test has poor sensitivity and specificity for diagnosing small bowel bacterial overgrowth (SBBO) 1
- The test may be confounded by variability in intestinal transit time 1
- A positive test result may not necessarily confirm the presence of SIBO, and a negative test result may not exclude the diagnosis 1
- The test may be more useful in patients with a high pretest probability of SIBO, such as those with anatomical abnormalities or prior small bowel surgery 1 It is also important to note that the lactulose breath test is not the only diagnostic tool available for SIBO, and other tests such as glucose breath testing or culture of small bowel aspirates may also be used 1. However, the lactulose breath test remains a commonly used and relatively non-invasive test for diagnosing SIBO.
From the Research
Breath Testing for Small Intestinal Bacterial Overgrowth
- The lactulose breath test is a non-invasive diagnostic modality for suspected small intestinal bacterial overgrowth (SIBO) 2, 3.
- Lactulose is a carbohydrate that is not absorbed in the small intestine and is used as a substrate in hydrogen breath testing for SIBO 2, 3.
- The test involves drinking a lactulose solution and then measuring the amount of hydrogen in the breath at regular intervals 3, 4.
- A positive test result is typically indicated by an increase in hydrogen levels of ≥20 ppm within 90 minutes of lactulose ingestion 3.
- The lactulose breath test is considered a useful diagnostic tool for SIBO, but its accuracy can be affected by factors such as accelerated mouth-to-caecum transit time 5.
- Some studies have proposed new criteria for interpreting the lactulose breath test to improve its specificity for SIBO diagnosis 4.
Preparation and Interpretation of Lactulose Breath Test
- The lactulose breath test typically involves ingesting a 10g dose of lactulose 3, 4.
- The test should be performed after an overnight fast and with proper patient preparation to minimize false positive results 2, 3.
- The interpretation of the test results should take into account the timing of the hydrogen peak and the magnitude of the increase in hydrogen levels 3, 4.
- A rise in hydrogen of ≥20 ppm from baseline within 90 minutes of lactulose ingestion is considered a positive result for SIBO 3.