Diagnosis of Small Intestinal Bacterial Overgrowth: Does Glucose Breath Testing Measure Up?

Abstract

Purpose: There is uncertainty regarding the best diagnostic approach for small intestinal bacterial overgrowth (SIBO). Our aim was to determine the reliability of glucose breath testing (GBT) for the diagnosis of SIBO relative to duodenal aspirate/cultures. Methods: A cohort of 14 patients with unexplained gas, bloating and abdominal discomfort and normal endoscopy and abdominal CT scan, underwent GBT and distal duodenal aspiration/culture in succession. Breath samples were assessed for hydrogen and methane levels at baseline and at 15 minute intervals for a 2 hour period using a Quintron Microanalyzer after an oral dose of 75gm glucose. Testing was deemed positive for SIBO if hydrogen levels increased ≥ 20ppm or methane levels ≥ 15ppm from baseline values. Patients also underwent esophagogastroduodenoscopy with aspiration of duodenal fluid from third/fourth portions of the duodenum using a 2mm Liguory catheter, under aseptic techniques for bacterial and fungal cultures. Bacterial cultures demonstrating ≥ 103 CFU/ml were considered positive for SIBO. Patients with fungal cultures showing ≥ +1 growth of candida were diagnosed with small intestinal fungal overgrowth (SIFO). The validity of GBT for the diagnosis of SIBO was determined using a 2x2 table and by calculating the sensitivity, specificity, and the positive and negative predictive values. Results: Duodenal aspirates showed a positive culture for SIBO in 5/14 (36%) patients, SIFO in 7/14 (50%) patients, and SIBO/SIFO in 3/14 (21%) patients. Bacterial cultures yielded Escherichia coli, alpha-haemolytic streptococcus, Staphylococcus aureus, Klebsiella pneumoniae, and gram-positive bacillus. GBT was positive for SIBO in 3 (21%) patients. The sensitivity and specificity of GBT for SIBO were 60% (14-95%, 95% CI) and 100% (66-100%, 95% CI), respectively. The positive predictive value was 100% (30-100%, 95% CI) and the negative predictive value was 82% (48-98%, 95% CI). Conclusion: Aspiration/culture of small bowel fluid appears to be the optimal testing modality for accurately detecting SIBO, but needs confirmation in a larger cohort. GBT has high specificity and lower sensitivity and does not detect SIFO. However, GBT is less invasive and less costly, therefore, it could be a first step in the diagnosis of SIBO.