Serum Potassium and Outcomes in CKD: Insights from the RRI-CKD Cohort Study

Background and objectives: The relationship between serum potassium (S-kappa) and mortality in chronic kidney disease (CKD) has not been systematically investigated. Design, setting, participants, & measurements: We examined the predictors and mortality association of S-kappa in the Renal Research Institute CKD Study cohort, wherein 820 patients with CKD were prospectively followed at four US centers for an average of 2.6 years. Predictors of S-kappa were investigated using linear and repeated measures regression models. Associations between S-kappa and mortality, the outcomes of ESRD, and cardiovascular events in time-dependent Cox models were examined. Results: The mean age was 60.5 years, 80% were white, 90% had hypertension, 36% had diabetes, the average estimated GFR was 25.4 ml/min per 1.73 m(2), and mean baseline S-kappa was 4.6 mmol/L. Higher S-kappa was associated with male gender, lower estimated GFR and serum bicarbonate, absence of diuretic and calcium channel blocker use, diabetes, and use of angiotensin-converting enzyme inhibitors and/or statins. A U-shaped relationship between S-kappa and mortality was observed, with mortality risk significantly greater at S-kappa <= 4.0 mmol/L compared with 4.0 to 5.5 mmol/L. Risk for ESRD was elevated at S-kappa <= 4 mmol/L in S-kappa categorical models. Only the composite of cardiovascular events or death as an outcome was associated with higher S-kappa (>= 5.5) Conclusions: Although clinical practice usually emphasizes greater attention to elevated S-kappa in the setting of CKD, our results suggest that patients who have CKD and low or even low-normal S-kappa are at higher risk for dying than those with mild to moderate hyperkalemia. Clin J Am Soc Nephrol 5: 762-769, 2010. doi: 10.2215/CJN.05850809