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

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.

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.

At baseline, median mGFR was 38.4 mL/min/1.73m²; 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/1.73m² 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 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 P_K 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.

In these patients under nephrology care, neither low nor high P_K was associated with excess mortality.