Lactulose Breath Test

Small intestinal bacterial overgrowth (SIBO) is the presence of overabundant bacteria in the small intestine. Intestinal bacteria produce hydrogen and methane gas during digestion of carbohydrates and fats. Too many bacteria can lead to excessive gas production that causes bloating, abdominal discomfort, and sometimes diarrhea or constipation. SIBO is one of the causes of irritable bowel syndrome. 

The gases produced by intestinal bacteria are absorbed by the intestines, enter the bloodstream, and are transported to the lungs, where they are exhaled. This is the basis of the lactulose breath test. 

Lactulose is poorly absorbed in the gastrointestinal tract, making it ideal for testing bacterial overgrowth throughout the intestine. The lactulose breath test measures the amount of hydrogen that a person exhales after drinking a mixture of glucose and water.

Patients should not have any fiber or fermentable foods in their intestines at the time of the test. Starting 24 hours before the test, they should eat only meat, poultry, fish, seafood, steamed white rice, eggs, or clear broth. They can drink plain black coffee, black tea and water. They should not take antibiotics, probiotics or colonoscopy prep for 4 weeks prior to the test. Laxatives, fiber supplements, and diarrhea medications should be avoided for 4 days before the test.

Patients should not eat, drink, or smoke for 12 hours before the test. Upon arrival, patients breathe into a collection bag. Then, they are then asked to drink 8 ounces of lactulose solution. A breath sample is collected every 15 to 20 minutes over a three hour period. 

The results of the timed samples collected after the lactulose ingestion are compared to the baseline sample. A typical fasting breath sample contains very low levels of hydrogen. Patients with bacterial overgrowth will ferment the lactulose, resulting in a rapid rise in exhaled hydrogen. A rapid rise in exhaled hydrogen is consistent with bacterial overgrowth. 

References

Lim J, Rezaie A. Pros and Cons of Breath Testing for Small Intestinal Bacterial Overgrowth and Intestinal Methanogen Overgrowth. Gastroenterol Hepatol (N Y). 2023 Mar;19(3):140-146.

Hasler WL, Lactulose breath testing, bacterial overgrowth, and IBS: just a lot of hot air?Gastroenterology, 2003;125(6):1898-1900.