Supplementary Material for: Serum Sodium Levels and Patient Outcomes in an Ambulatory Clinic-Based Chronic Kidney Disease Cohort

<b><i>Background: </i></b>Chronic kidney disease (CKD) patients are prone to both hypo- and hypernatremia. Little has been published on the epidemiology of hypo- and hypernatremia in ambulatory patients with non-dialysis CKD. <b><i>Methods:</i></b> Data collected in two contemporaneous CKD cohort studies, the Renal Research Institute (RRI)-CKD study (n = 834) and the Study of Treatment of Renal Insufficiency: Data and Evaluation (STRIDE) (n = 1,348) were combined and analyzed to study the association between serum sodium (Na<sup>+</sup>) and clinical outcomes. <b><i>Results:</i></b> Baseline estimated glomerular filtration rate (eGFR) and Na<sup>+</sup> were 26 ± 11 ml/min/1.73 m<sup>2</sup> and 140.2 ± 3.4 mEq/l, respectively. The prevalence of Na<sup>+</sup> ≤135 mEq/l and ≥144 mEq/l was 6 and 16%, respectively. Higher baseline Na<sup>+</sup> was significantly associated with male sex, older age, systolic blood pressure, BMI, serum albumin, presence of heart failure, and lower eGFR. The risk of end-stage renal disease (ESRD) was marginally significantly higher among patients with Na<sup>+</sup> ≤135 mEq/l, compared with 140< Na<sup>+</sup> <144 mEq/l (referent), in time-dependent models (adjusted hazard ratio, HR = 1.52, p = 0.06). Mortality risk was significantly greater at 135< Na<sup>+</sup> ≤140 mEq/l (adjusted HR = 1.68, p = 0.02) and Na<sup>+</sup> ≥144 mEq/l (adjusted HR = 2.01, p = 0.01). <b><i>Conclusion:</i></b> CKD patients with Na<sup>+</sup> ≤135 mEq/l were at a higher risk for progression to ESRD, whereas both lower and higher Na<sup>+</sup> levels were associated with a higher risk of mortality. While caring for CKD patients, greater attention to serum sodium levels by clinicians is warranted and could potentially help improve patient outcomes.