Plasma potassium ranges associated with mortality across stages of chronic kidney disease: the Stockholm CREAtinine Measurements (SCREAM) project

BACKGROUND: Small-scale studies suggest that hyperkalaemia is a less threatening condition in chronic kidney disease (CKD), arguing adaptation/tolerance to potassium (K(+)) retention. This study formally evaluates this hypothesis by estimating the distribution of plasma K(+) and its association with mortality across CKD stages. METHODS: This observational study included all patients undergoing plasma K(+) testing in Stockholm during 2006–11. We randomly selected one K(+) measurement per patient and constructed a cross-sectional cohort with mortality follow-up. Covariates included demographics, comorbidities, medications and estimated glomerular filtration rate (eGFR). We estimated K(+) distribution and defined K(+) ranges associated with 90-, 180- and 365-day mortality. RESULTS: Included were 831 760 participants, of which 70 403 (8.5%) had CKD G3 (eGFR <60–30 mL/min) and 8594 (1.1%) had CKD G4–G5 (eGFR <30 mL/min). About 66 317 deaths occurred within a year. Adjusted plasma K(+) increased across worse CKD stages: from median 3.98 (95% confidence interval 3.49–4.59) for eGFR >90 to 4.43 (3.22–5.65) mmol/L for eGFR ≤15 mL/min/1.73 m(2). The association between K(+) and mortality was U-shaped, but it flattened at lower eGFR strata and shifted upwards. For instance, the range where the 90-day mortality risk increased by no more than 100% was 3.45–4.94 mmol/L in eGFR >60 mL/min, but was 3.36–5.18 in G3 and 3.26–5.53 mmol/L in G4–G5. In conclusion, CKD stage modifies K(+) distribution and the ranges that predict mortality in the community. CONCLUSION: Although this study supports the view that hyperkalaemia is better tolerated with worse CKD, it challenges the current use of a single optimal K(+) range for all patients.