Association of plasma potassium with mortality and end-stage kidney disease in patients with chronic kidney disease under nephrologist care - The NephroTest study

Background: Low and high blood potassium levels are common and were both associated with poor outcomes in patients with chronic kidney disease (CKD). Whether such relationships may be altered in CKD patients receiving optimized nephrologist care is unknown. Methods: NephroTest is a hospital-based prospective cohort study that enrolled 2078 nondialysis patients (mean age: 59 +/- 15 years, 66% men) in CKD stages 1 to 5 who underwent repeated extensive renal tests including plasma potassium (P-K) and glomerular filtration rate (GFR) measured (mGFR) by 51Cr-EDTA renal clearance. Test reports included a reminder of recommended targets for each abnormal value to guide treatment adjustment. Main outcomes were cardiovascular (CV) and all-cause mortality before end-stage kidney disease (ESKD), and ESKD. Results: At baseline, median mGFR was 38.4 mL/min/1.73m(2); prevalence of low P-K (<4 mmol/L) was 26.5%, and of high P-K (>5 mmol/L) 6.4%; 74.4% of patients used angiotensin converting enzyme inhibitors (ACEi) or angiotensin receptor blockers (ARB). After excluding 137 patients with baseline GFR <10 mL/min/1.73m(2) or lost to follow-up, 459 ESKD events and 236 deaths before ESKD (83 CV deaths) occurred during a median follow-up of 5 years. Compared to patients with P-K within [4, 5] mmol/L at baseline, those with low P-K had hazard ratios (HRs) [95% CI] for all-cause and CV mortality before ESKD, and for ESKD of 0.82 [0.58-1.16], 1.01 [0.52-1.95], and 1.14 [0.89-1.47], respectively, with corresponding figures for those with high PK of 0.79 [0.48-1.32], 1.5 [0.69-3.3], and 0.92 [0.70-1.21]. Considering time-varying P-K did not materially change these findings, except for the HR of ESKD associated with high P-K, 1.39 [1.09-1.78]. Among 1190 patients with at least two visits, P-K had normalized at the second visit in 39.9 and 54.1% respectively of those with baseline low and high P-K. Among those with low P-K that normalized, ARB or ACEi use increased between the visits (68.3% vs 81.8%, P < .0001), and among those with high P-K that normalized, potassium-binding resin and bicarbonate use increased (13.0% vs 37.0%, P < .001, and 4.4% vs 17.4%, P = 0.01, respectively) without decreased ACEi or ARB use. Conclusion: In these patients under nephrology care, neither low nor high P-K was associated with excess mortality.