Exhaled Hydrogen as a Marker of Intestinal Fermentation Is Associated with Diarrhea in Kidney Transplant Recipients

Diarrhea is common among kidney transplant recipients (KTR). Exhaled hydrogen (H₂) is a surrogate marker of small bowel dysbiosis, which may drive diarrhea. We studied the relationship between exhaled H₂ and diarrhea in KTR, and explored potential clinical and dietary determinants.

Clinical, laboratory, and dietary data were analyzed from 424 KTR participating in the TransplantLines Biobank and Cohort Study (NCT03272841). Fasting exhaled H₂ concentration was measured using a model DP Quintron Gas Chromatograph. Diarrhea was defined as fast transit time (types 6 and 7 according to the Bristol Stool Form Scale, BSFS) of 3 or more episodes per day. We studied the association between exhaled H₂ and diarrhea with multivariable logistic regression analysis, and explored potential determinants using linear regression.

KTR (55.4 ± 13.2 years, 60.8% male, mean eGFR 49.8 ± 19.1 mL/min/1.73 m²) had a median exhaled H₂ of 11 (5.0-25.0) ppm. Signs of small intestinal bacterial overgrowth (exhaled H₂ ≥ 20 ppm) were present in 31.6% of the KTR, and 33.0% had diarrhea. Exhaled H₂ was associated with an increased risk of diarrhea (odds ratio 1.51, 95% confidence interval 1.07-2.14 per log₂ ppm, p = 0.02). Polysaccharide intake was independently associated with higher H₂ (std. β 0.24, p = 0.01), and a trend for an association with proton-pump inhibitor use was observed (std. β 0.16 p = 0.05).

Higher exhaled H₂ is associated with an increased risk of diarrhea in KTR. Our findings set the stage for further studies investigating the relationship between dietary factors, small bowel dysbiosis, and diarrhea after kidney transplantation.