Emergency department referral and short-term death after outpatient hyperkalemia: a population-based study.

BACKGROUND: Hyperkalemia can be deadly, yet clinical decision-making for outpatient management is unclear. We sought to determine whether an emergency department encounter within 24 hours of a severe outpatient hyperkalemia result was associated with lower rates of immediate and short-term all-cause death. METHODS: We conducted a retrospective population-based cohort study in Ontario, Canada, involving adults (age ≥18 yr) with an outpatient potassium result greater than 6.2 mmol/L from Jan. 1, 2007, to Dec. 24, 2021. Patients who presented to the emergency department were propensity matched (1:1) to patients who did not. We estimated risk ratios and risk differences for all-cause death within 1, 3, and 7 days after the encounter. We performed subgroup analyses based on kidney function, sex, diabetes, renin-angiotensin-aldosterone inhibitor use, potassium level, and ordering physician specialty. RESULTS: A total of 57 607 individuals had an outpatient potassium result greater than 6.2 mmol/L. Among these individuals, 7469 emergency department encounters occurred. After matching, 6557 patients had an emergency department encounter and 6557 did not. Within 7 days, a total of 209 deaths (1.6%) occurred. The risk of death was significantly lower among those with an emergency department encounter at 1 day (risk ratio [RR] 0.39, 95% confidence interval [CI] 0.24 to 0.65), 3 days (RR 0.47, 95% CI 0.32 to 0.67), and 7 days (RR 0.69, 95% CI 0.52 to 0.90). Subgroup analysis showed the greatest mortality reduction among patients with higher potassium levels (>6.6 mmol/L) and impaired kidney function (estimated glomerular filtration rate <30 mL/min/1.73 m2). INTERPRETATION: Presentation to the emergency department within 24 hours of a severe outpatient hyperkalemia result is associated with lower rates of immediate and short-term death. These findings support urgent emergency department referrals and underscore the need for standardized reporting and management guidelines.