Background: Data on the true burden of hyperkalemia (HK) in patients with chronic kidney disease (CKD) in a real-world setting are scarce.

Methods: The incidence rate of HK [first blood test with an elevated blood potassium level level >5.0 mmol/L] in primary or hospital care was assessed in a population-based cohort of all newly diagnosed CKD patients [second estimated glomerular filtration rate (eGFR) measurement <60 mL/min/1.73 m 2 or hospital diagnosis] in northern Denmark. Risk factors and clinical outcomes were compared for CKD patients with HK and matched CKD patients without HK.

Results: Of 157 766 patients with CKD, 28% experienced HK, for an overall HK incidence rate of 70/1000 person-years. Among patients with Stage 3A, 3B, 4 or 5 CKD, 9, 18, 31 and 42%, respectively, experienced HK within the first year. Important HK risk factors included diabetes {prevalence ratio [PR] 1.74 [95% confidence interval (CI) 1.69-1.79]}, heart failure [PR 2.31 (95% CI 2.23-2.40)] and use of angiotensin-converting enzyme inhibitors [PR 1.45 (95% CI 1.42-1.48)], potassium supplements [PR 1.59 (95% CI 1.55-1.62)] or spironolactone [PR 2.53 (95% CI 2.44-2.63)]. In CKD patients who developed HK, 34% had any acute hospitalization 6 months before the HK event, increasing to 57% 6 months after HK [before-after risk ratio 1.72 (95% CI 1.69-1.74)]. The 6-month mortality following HK was 26%, versus 6% in matched non-HK patients. Compared with non-HK patients, 6-month hazard ratios for any acute hospitalization in HK patients were 2.11-fold higher, including hazard ratios of 2.07 for cardiac diagnoses, 2.29 for ventricular arrhythmias, 3.26 for cardiac arrest, 4.77 for intensive care and 4.85 for death.

Conclusions: More than one in four CKD patients develops HK. Patients with severe CKD, diabetes, heart failure or use of spironolactone are at high risk. HK is associated with severe clinical outcomes.