Prevalence of Hyperkalemia in a Contemporary European Cohort According to EKFC eGFR Categories

Background/Objectives: Hyperkalemia is common in patients with chronic kidney disease (CKD). However, its epidemiology may be evolving due to population aging, new therapeutic developments and novel estimated glomerular filtration rate (eGFR) equations. We have re-evaluated the epidemiology of hyperkalemia in a contemporary cohort in which eGFR was assessed using the EKFC equation recommended by the European Federation of Clinical Chemistry and Laboratory Medicine (EFLM). Methods: We analyzed 190,579 laboratory tests with serum potassium values corresponding to individual outpatients in Primary or Specialty Care from a single laboratory in 2023, representing 42% of the catchment area population. Results: Hypokalemia (<3.5 mmol/L) was present in 0.3% patients, hyperkalemia (≥5.0 mmol/L) in 10.5% (11.5% of men, 9.7% of women). Hyperkalemia was mostly mild (9.4%) but was severe in 0.1% overall and in 10.5% of CKD G5. One in four patients with hyperkalemia had CKD. Hyperkalemia was more common among patients with CKD G3-G5 defined using the CKD-EPI2009 equation than defined using the EKFC equation (20.5 vs. 18.6%, p < 0.0001). Using EKFC, hyperkalemia prevalence increased with decreasing eGFR from G1 (6.6%) to G2 (10.8%) and, especially in CKD G3-G5 (G3 17.2% to G5 47.5%). In multivariate logistic analysis, worse renal function, worse diabetes control, older age, and surrogates for release of intracellular potassium during sample processing (red blood cell counts or size, platelet counts, elevated calcium levels) were independently associated with hyperkalemia. This multivariate model yielded an area under the curve (AUC) of the Receiver Operating Characteristic (ROC) curve for hyperkalemia of 0.678 (95% CI 0.674-0.682). Random forest also identified GFR as the most important feature associated with hyperkalemia and generally concurred with logistic analysis findings. Conclusions: Hyperkalemia remains common, especially in CKD G5. While hyperkalemia is mainly associated with low eGFR, sample processing should be optimized.