P2486 - Commercial Breath Testing Underestimates Intestinal Methanogenic Overgrowth: Application of the American College of Gastroenterology Small Intestinal Bacterial Overgrowth (SIBO) Guideline

Joy Liu, MD¹, Emerald Adler, MSW¹, Elyse Linson, MD, MPH¹, Darren M. Brenner, MD^2
1McGaw Medical Center of Northwestern University, Chicago, IL; ²Northwestern University Feinberg School of Medicine, Chicago, IL

Introduction: The American College of Gastroenterology (ACG) guideline defines a positive breath test (BT) as a rise in hydrogen (H₂) from baseline of ≥20 parts per million (p.p.m.) within 90 minutes for SIBO or a methane (CH₄) level ≥10 p.p.m. at any time for intestinal methanogenic overgrowth (IMO). However, these consensus thresholds may not be reflected in commercial analyses. We compared the accuracy between commercial and clinical BT interpretation using the ACG thresholds as the gold standard. Inter-rater reliability (IRR) between clinicians was also assessed.

Methods: Three clinicians (GI faculty, senior and junior GI fellow) at an academic medical center independently reviewed BT obtained as part of a standard clinical diagnostic workup from Commonwealth Diagnostics International. A sample of 20 BT were used as a training module. “Positive” and “negative” results were compared to commercial reports of “supported” or “not supported” for H₂ and CH₄. Tests of accuracy and statistical analysis including IRR among GI faculty and fellows was calculated using Kripendorff’s alpha coefficient reliability test in SPSS.

Results: 582 consecutive glucose (N=534) and lactulose (N=48) BT were included. 202 BT were defined as positive by ACG criteria, whereas 116 were reported as positive by commercial interpretation. The majority of the discrepancy stemmed from differing interpretations of CH₄ results. Concordance for H₂ positivity was high (94%) but poor for methane (41.3%). (Figure) Approximately 40% (N=151) of BT failed to detect H₂ or CH₄. Excluding these, commercial interpretation had a sensitivity of 55%, specificity of 98%, negative predictive value of 71%, and positive predictive value of 96%. IRR between GI faculty and fellows was high: a=0.9050 (95% CI 0.88-0.93).

Discussion: Commercial BT interpretation underrepresents IMO. Clinician use of ACG criteria identified similar numbers of H₂-positive BT, but increased CH₄ positivity. Clinicians utilizing ACG guideline thresholds should be aware of potentially misleading commercial interpretations. High overall IRR suggests that interpretations using ACG criteria are reproducible regardless of level of training.


Figure: Positive BT by ACG guideline compared to commercial report

	ACG Criteria	Commonwealth Diagnostics International
H2	Change from baseline ≥20 p.p.m. within 90 minutes	Change from baseline ≥20 p.p.m. within 90 minutes
CH4	Level ≥10 p.p.m. at any point	Change from baseline ≥10 p.p.m. within 90 minutes

Table: Comparison of ACG criteria to commercial breath test criteria for positive diagnosis of intestinal bacterial overgrowth


Disclosures:
Joy Liu indicated no relevant financial relationships.
Emerald Adler indicated no relevant financial relationships.
Elyse Linson indicated no relevant financial relationships.
Darren Brenner indicated no relevant financial relationships.


Joy Liu, MD¹, Emerald Adler, MSW¹, Elyse Linson, MD, MPH¹, Darren M. Brenner, MD². P2486 - Commercial Breath Testing Underestimates Intestinal Methanogenic Overgrowth: Application of the American College of Gastroenterology Small Intestinal Bacterial Overgrowth (SIBO) Guideline, ACG 2021 Annual Scientific Meeting Abstracts. Las Vegas, Nevada: American College of Gastroenterology.