AbstractBackgroundLow 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.MethodsNephroTest 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 (PK) 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.ResultsAt baseline, median mGFR was 38.4 mL/min/1.73m2; prevalence of low PK (<4 mmol/L) was 26.5%, and of high PK (>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/1.73m2 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 PK within [4, 5] mmol/L at baseline, those with low PK 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 PK did not materially change these findings, except for the HR of ESKD associated with high PK, 1.39 [1.09–1.78]. Among 1190 patients with at least two visits, PK had normalized at the second visit in 39.9 and 54.1% respectively of those with baseline low and high PK. Among those with low PK that normalized, ARB or ACEi use increased between the visits (68.3% vs 81.8%, P < .0001), and among those with high PK 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.ConclusionIn these patients under nephrology care, neither low nor high PK was associated with excess mortality.