“Best Practice Advice” for Small Intestinal Bacterial Overgrowth– ????

EMM Quigley, JA Murray, M Pimental. Gastroenterol 2020; 159: 1526-1532. Clinical Practice Guidelines. Full Free Text: AGA Clinical Practice Update on Small Intestinal Bacterial Overgrowth: Expert Review

This is a really lousy clinical practice guideline but a pretty good review of small intestinal bacterial overgrowth (SIBO). The reason why it is lousy: it provides virtually no recommendations on how to define/diagnose SIBO, does not recommend specific testing and equivocates on specific treatments.

Here are a few of the “best practice advice” as examples:

  • #1 The definition of SIBO as a clinical entity lacks precision and consistency; it is a term generally applied to a clinical disorder where symptoms, clinical signs, and/or laboratory abnormalities are attributed to changes in the numbers of bacteria or in the composition of the bacterial population in the small intestine
  • #5 A major impediment to our ability to accurately define SIBO is our limited understanding of normal small intestinal microbial populations
  • #6 Controversy remains concerning the role of SIBO in the pathogenesis of common functional symptoms, such as those regarded as components of irritable bowel syndrome
  • #9 There is a limited database to guide the clinician in developing antibiotic strategies for SIBO

While not providing ‘best practical advice,’ the article does provide details regarding limitations in testing, underlying pathogenesis, and potential treatment regimens for adults.

Table 3 -Provides Some Takeaway Points

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Breath Test Reliability for Bacterial Overgrowth

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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Flamenco Beach, Culebra

Flamenco Beach, Culebra