While breath test reliability for bacterial overgrowth has been a concern for a long time, another study (EC Lin, BT Massey. Clin Gastroenterol Hepatol 2016; 14: 203-08) takes a new approach to show that the glucose breath tests are subject to a high false-positive rate. This is often related to rapid transit time.
Here’s what they did:
In a retrospective study, they examined data from 139 patients with suspected small bowel bacterial overgrowth (SBBO) (2003-2013). Abnormal glucose breath tests were indicated by either hydrogen or methane >15 parts per million within 90 minutes after glucose ingestion. In addition, they used concurrent scintigraphy (by labeling glucose with a Tc99m compound) to determine whether this increase occurred before or after glucose bolus arrived in the cecum.
- 46 (33%) had abnormal breath tests. Of these 22 (48%) had false-positive results due to colonic fermentation.
- False-positives were higher (65%) in the subset of patients with prior upper gastrointestinal surgery. The nonsurgical group had a 13% false-positive rate.
- This study shows that with rapid transit, significant glucose malabsorption is possible.
Because direct culture of small bowel contents is expensive, invasive and subject to contamination, physicians have relied on breath tests for diagnosis of SBBO or have empirically treated for SBBO. The discussion and related editorial (pg 209) explain that lactulose breath testing is not more reliable than glucose breath testing.
My take: For patients with prior GI surgery (who are at the highest risk for SBBO), breath testing may not be more reliable than flipping a coin. True positive results are more likely if hydrogen peak occurs within 60 minutes of glucose administration.
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