From the Guidelines
The most accurate way to diagnose Small Intestinal Bacterial Overgrowth (SIBO) is through a small intestinal aspirate and culture, which is considered the gold standard. This procedure involves collecting fluid samples directly from the small intestine during an endoscopy and then culturing them to identify bacterial growth. A bacterial count exceeding 10^3 colony-forming units per milliliter is typically diagnostic of SIBO 1. However, due to its invasive nature, cost, and limited availability, breath tests are more commonly used in clinical practice.
Diagnosis Methods
- The hydrogen and methane breath tests involve drinking a sugar solution (typically lactulose or glucose) and measuring the gases produced by bacterial fermentation in breath samples collected over 2-3 hours.
- Glucose breath tests are more specific but may miss distal SIBO, while lactulose tests can detect distal SIBO but have higher false positive rates.
- Preparation for breath testing requires a specific diet the day before (avoiding complex carbohydrates and fiber), fasting for 12 hours, and avoiding antibiotics for 2-4 weeks prior.
Recent Guidelines
According to the 2018 guidelines for the investigation of chronic diarrhoea in adults by the British Society of Gastroenterology, both glucose and lactulose hydrogen breath tests have poor sensitivity and specificity and are not recommended for the diagnosis of small bowel bacterial overgrowth 1. The utility of concurrent hydrogen and methane breath testing with measurements of orocaecal transit time could reduce a false positive diagnosis due to variability in intestinal transit, but has not been subject to definitive clinical study hence cannot be recommended 1.
Clinical Practice
In clinical practice, a small intestinal aspirate and culture is the most accurate method for diagnosing SIBO, but due to its limitations, other methods such as breath tests may be used, taking into account their limitations and the need for proper preparation and interpretation 1.
From the Research
Diagnosis of SIBO
The diagnosis of Small Intestinal Bacterial Overgrowth (SIBO) can be challenging due to the lack of standardization of tests and their interpretation 2. Several tests have been proposed, including:
- Glucose breath test
- Lactulose breath test
- Small intestinal aspiration and culture
Most Accurate Diagnostic Method
According to the available evidence, the most accurate method for diagnosing SIBO is the glucose breath test (GBT) 3. The GBT is recommended for use in appropriately chosen patients, and the lactulose breath test (LBT) should be discarded due to its incorrect premise and potential for over-diagnosis of SIBO.
Limitations of Diagnostic Methods
The culture of intestinal aspirates is considered the gold standard for SIBO diagnosis, but it has limitations such as high costs and invasivity, making it impractical for clinical use 4. Hydrogen breath tests, including the GBT, are widely used due to their low costs, non-invasivity, and sufficient accuracy and reproducibility.
Clinical Practice
In clinical practice, SIBO should be suspected in patients with IBS-like symptoms and/or malabsorption syndrome, particularly in the presence of disorders predisposing to SIBO development 4. The most common diagnostic tool is the hydrogen breath test, which can help identify patients with SIBO and guide treatment decisions 5, 6.