Association of eGFR and mortality with use of a joint model: results of a nationwide study in Iceland

OBJECTIVES: Prior studies on the association of estimated glomerular filtration rate (eGFR) and mortality have failed to include methods to account for repeated eGFR determinations. The aim of this study was to estimate the association between eGFR and mortality in the general population in Iceland employing a joint model. METHODS: We obtained all serum creatinine and urine protein measurements from all clinical laboratories in Iceland in the years 2008–16. Clinical data were obtained from nationwide electronic medical records. eGFR was calculated using the Chronic Kidney Disease Epidemiology Collaboration equation and categorized as follows: 0–29, 30–44, 45–59, 60–74, 75–89, 90–104 and >104 mL/min/1.73 m(2). A multiple imputation method was used to account for missing urine protein data. A joint model was used to assess risk of all-cause mortality. RESULTS: We obtained 2 120 147 creatinine values for 218 437 individuals, of whom 84 364 (39%) had proteinuria measurements available. Median age was 46 (range 18–106) years and 47% were men. Proteinuria associated with increased risk of death for all eGFR categories in persons of all ages. In persons ≤65 years, the lowest risk was observed for eGFR of 75–89 mL/min/1.73 m(2) without proteinuria. For persons aged >65 years, the lowest risk was observed for eGFR of 60–74 mL/min/1.73 m(2) without proteinuria. eGFR of 45–59 mL/min/1.73 m(2) without proteinuria did not associate with increased mortality risk in this age group. eGFR >104 mL/min/1.73 m(2) associated with increased mortality. CONCLUSIONS: These results lend further support to the use of age-adapted eGFR thresholds for defining chronic kidney disease. Very high eGFR needs to be studied in more detail with regard to mortality.