Bowel Habits and the Association With Uremic Toxins in Non–Dialysis-Dependent Chronic Kidney Disease Patients

Objective: The aim of this study is to evaluate the association between bowel habits and microbial-derived uremic toxins p-cresyl sulfate (PCS) and indoxyl sulfate (IS) in patients with non–dialysis-dependent chronic kidney disease (NDD-CKD). Design and Methods: This is a cross-sectional analysis including 43 nondiabetic NDD-CKD patients (58% men; 59.0 ± 13.5 years; estimated glomerular filtration rate, 21.3 ± 7.9 mL/min/1.73 m²). Bowel habit was assessed by the Bristol Stool Scale (BSS <3, characterized by hard consistency of stools and/or low frequency of evacuation and BSS ≥3, representing a more regular bowel habit) and by the Rome III criteria. PCS and IS (serum, free and total; urinary, total) were determined by high-performance liquid chromatography. Dietary intake was assessed by the 3-day food records. Results: The frequency of constipation assessed by BSS and Rome III criteria was 33% (n = 14/43) and 35% (n = 15/43), respectively. The BSS <3 exhibited higher PCS, independent of renal function and dietary protein-fiber ratio (β [95% confidence interval {CI}]: serum, total PCS = 1.54 [1.06-2.23], P =.02; serum free PCS = 1.40 [1.00-1.97], P =.05; urinary PCS = 1.78 [1.10-2.90], P <.02). According to the Rome III criteria, a tendency for a higher serum total PCS (β [95% CI]: 1.39 [0.95-2.03 μmol/L], P =.09) and a significantly higher urinary PCS (β [95% CI]: 1.80 [1.11-2.94 μmol/24 h], P =.02) was found in constipated participants. No effect of a compromised bowel habit (Rome III criteria or BSS) was found on IS. Conclusion: Constipation may lead to production of PCS in nondiabetic NDD-CKD patients.