MO517EFFECT MODIFIERS OF SERUM POTASSIUM AND MORTALITY IN THE IRISH HEALTH SYSTEM: THE NATIONAL KIDNEY DISEASE SURVEILLANCE SYSTEM (NKDSS)

Abstract

Abstract Background and Aims Serum potassium (K+) exhibits a u-shaped association with mortality but uncertainty exists regarding optimal thresholds for survival and influencing factors. We examined the impact of serum K* on mortality in the Irish Health System with particular focus on kidney function and location of medical supervision. Method We utilised data from the Irish Kidney Disease Surveillance System (NKSS) to explore the association of serum K+ and mortality in a longitudinal cohort study. We identified all adult individuals (age > 18 years) who accessed health care from 2007 and 2012 in a regional health system with complete data on serum K+, associated laboratory indicators and vital status up to 31st December 2013 (n = 32,643). We randomly selected a single K+ measurement per patient with date of measurement as index date. Chronic kidney disease was defined as eGFR <60ml/min/1.73m² vs greater recorded at index date. Location of medical supervision was recorded as emergency room, inpatient location; outpatient clinic, and general practice location. The association of serum K+ was explored in categories and as a continuous variable in restricted cubic splines with mortality. Multivariable Cox regression determined hazard ratios and 95% confidence intervals with adjustment for baseline health indicators. Results Mean age was 57.1 years, 5,056 died (15.4%) with a median follow-up of 5.1 years. With adjustment, for age, sex, baseline health status, and location of medical supervision, the pattern of mortality was non-linear and u-shaped with greatest risks for patients with extreme values. Modelled as a continuous variable, the serum K +thresholds for optimal survival were from 4.1 to 5.2 mmol/L. Compared to patients without baseline CKD, the risks were attenuated for patients with CKD (p-value interaction 0.012). The associated risk thresholds were wider for CKD patients with significant increased risk above 5.8 mmol/L whereas, for those without CKD, serum K +thresholds for optimal survival were between 4.2-5.4 mmol/L. Similarly, mortality patterns were greatly attenuated for patients who were managed in the outpatient and general practice locations (p-value interaction <0.001) than the emergency room or inpatient settings (Figure 1). Conclusion Risk thresholds for optimal survival for serum K+ vary according to CKD and location of medical supervision in real-world clinical cohorts. Better understanding of these thresholds and effect modifiers are essential for inform decision making and therapeutic interventions. Funding Source Health Research Board (HRB-SDAP-2019-036), Midwest Research and Education Foundation (MKid), Vifor Pharma.