Comparing the impact of older age on outcome in chronic kidney disease of different etiologies: a prospective cohort study

Background In older patients with chronic kidney disease (CKD), the risk of progression to end stage renal disease and cardiovascular death both differ compared to younger patients. This likely reflects differences in case mix and co-morbid burdens. We sought to establish the extent to which age itself is an independent biomarker of adverse outcome in CKD. Methods This was an analysis of the Salford Kidney Study, a prospective, longitudinal, observational study of 2,667 patients with eGFR < 60 ml/min/1.73 m2. Patients were divided into four age groups (< 55, 55–65, 65–75 and > 75 years). Within group adjusted hazard ratios for death in older compared to younger patients were calculated for different primary renal diseases. A competing risk model of death and renal replacement therapy (RRT) as outcomes was performed. Results The median age of the cohort was 67.1 years [interquartile range (IQR): 55.6–75.3] and median eGFR 30.8 ml/min/1.73 m2 (IQR: 20.6–43.2). Follow up was 3.5 ± 2.9 years. Overall, the adjusted HR for death in patients aged > 75 years compared to those < 55 years was 4.4 (95% CI 3.4–5.9), p < 0.001. The HR for death differed between primary renal diseases and CKD stages. In diabetic nephropathy, the HR was 3.0 (1.8–5.3, p < 0.001), in glomerulonephritis the HR was 12.2 (5.6–25.5, p < 0.001). The cumulative incidence of RRT was < 0.1 at 10 years for patients > 75 years, compared with 0.50 in those < 55 years. Death was more likely at 20 months in those aged 75 years or older (0.17) than at 10 years in those aged < 55 years (0.10). Conclusion This study demonstrates that the risk associated with older age shows significant variability between primary renal diseases. This is whilst acknowledging that observational studies carry the risk of hidden bias not adjusted for in the statistical model.