Hyperkalemia in Chronic Kidney Disease: A Nationwide Real-World Evidence Study From Finland

Rationale & Objective Hyperkalemia is common in chronic kidney disease (CKD) and associated with adverse outcomes and renin-angiotensin-aldosterone system inhibitor (RAASi) discontinuation, but comprehensive nationwide data are limited. We characterized hyperkalemia incidence, recurrence, treatment changes, and outcomes in Finnish CKD patients. Study Design Nationwide observational cohort study using linked Finnish healthcare registers (2014–2023). Setting & Participants 158,420 adults with confirmed CKD, defined as two eGFR values <60 mL/min/1.73 m 2 or two urine albumin-creatinine ratio values ≥3 mg/mmol ≥90 days apart, or kidney disease diagnosis with qualifying laboratory values. Exposure Hyperkalemia, defined as potassium ≥5.0 mmol/L or ICD-10 code E87.5. Outcomes All-cause mortality, major adverse cardiovascular events (MACE), all-cause and heart failure hospitalizations, and RAASi treatment changes. Analytical Approach Patients with hyperkalemia were matched 1:1 to comparisons without hyperkalemia using nearest-neighbour matching on eGFR, time since confirmed CKD, age, and sex (n=60,867 per cohort). Adjusted hazard ratios were estimated using Cox and Fine-Gray competing risk models. Results During median 3.5-year follow-up, 38.4% experienced hyperkalemia, with 59.7% recurrence within a median of 0.23 years. RAASi discontinuation was more frequent after hyperkalemia versus comparisons (14.6% vs 10.6%, p<0.001). Hyperkalemia was associated with higher one-year all-cause mortality (29.2% vs 19.4%; adjusted HR 1.60, 95% CI 1.56–1.64), MACE (15.0% vs 11.2%; HR 1.31, 95% CI 1.27–1.35), all-cause hospitalizations (57.2% vs 45.4%; HR 1.42, 95% CI 1.40–1.45), and heart failure hospitalizations (21.1% vs 13.4%; HR 1.52, 95% CI 1.48–1.57). Limitations Observational design with potential residual confounding despite matching and covariate adjustment; differential monitoring intensity may introduce surveillance bias. Conclusions Hyperkalemia affected more than one-third of CKD patients with high recurrence, and was associated with increased mortality, cardiovascular events, hospitalizations, and RAASi discontinuation, highlighting the need for optimal management strategies.