Many individuals with digestive issues wonder if a colonoscopy can detect Small Intestinal Bacterial Overgrowth (SIBO). SIBO involves an excessive growth of bacteria in the small intestine. A colonoscopy, however, visually examines the large intestine and rectum.
Understanding SIBO
Small Intestinal Bacterial Overgrowth (SIBO) is an abnormal increase in the bacterial population within the small intestine. The small intestine normally contains few bacteria compared to the large intestine. In SIBO, bacteria that typically reside in the large intestine, or an excessive amount of normally present bacteria, proliferate. This overgrowth interferes with normal digestion and nutrient absorption.
The Purpose of a Colonoscopy
A colonoscopy is a medical procedure that examines the inside of the large intestine, including the colon, rectum, and anus. A colonoscope, a long, flexible tube with a camera, is inserted through the rectum for a visual inspection of the bowel lining. This procedure primarily detects structural abnormalities.
Healthcare providers use colonoscopies to identify conditions like polyps, which are precancerous growths on the colon’s lining. It also detects inflammation, ulcers, or sources of bleeding, common in inflammatory bowel disease (Crohn’s disease or ulcerative colitis). The procedure allows for biopsies or the removal of abnormal growths.
Why Colonoscopy Does Not Detect SIBO
A colonoscopy is not designed to diagnose Small Intestinal Bacterial Overgrowth due to fundamental differences in what each targets. The colonoscope primarily visualizes the large intestine, while SIBO occurs in the small intestine. Although a small segment of the terminal ileum, the very end of the small intestine, might be briefly examined, this limited view is insufficient to assess bacterial overgrowth throughout the entire small intestine.
SIBO involves an overgrowth of microscopic bacteria, which are not visible structural abnormalities on the bowel lining. A colonoscopy is a visual inspection tool, identifying issues like polyps or inflammation. The inner lining of the small intestine can appear normal during a colonoscopy, even when a significant bacterial overgrowth is present. Therefore, a colonoscopy cannot directly detect the bacterial imbalance characteristic of SIBO.
Diagnosing SIBO
Since a colonoscopy does not detect SIBO, other specialized methods are used for diagnosis. The most common non-invasive approach is a breath test, which measures hydrogen and methane gases in exhaled breath. After consuming a sugar solution, such as glucose or lactulose, bacteria in the small intestine ferment the sugar and produce these gases. A rapid rise in hydrogen or methane levels indicates bacterial overgrowth. Specifically, a rise of 20 parts per million (ppm) of hydrogen or 10 ppm of methane from baseline within 90 minutes suggests SIBO.
Another diagnostic method, considered the “gold standard” for SIBO diagnosis, is a small bowel aspirate and culture. This invasive procedure involves an endoscopy where a thin, flexible tube is passed down the throat to the small intestine. A fluid sample is collected from the small intestine and sent to a laboratory to culture and count the bacteria present. A bacterial count exceeding 10^3 colony-forming units per milliliter in a duodenal aspirate indicates SIBO.
Clinical suspicion, based on a patient’s symptoms and medical history, also guides the diagnostic process. Symptoms such as bloating, abdominal pain, diarrhea, and unintentional weight loss can suggest SIBO. Sometimes, a positive response to antibiotic treatment further supports a SIBO diagnosis, even if test results are inconclusive.