New-onset anemia and associated risk of ESKD and death in non-dialysis CKD patients: a multicohort observational study

Background Anemia is a common complication of chronic kidney disease (CKD), but its incidence in nephrology settings is poorly investigated. Similarly, the risks of adverse outcomes associated with new-onset anemia are not known. Methods We performed a pooled analysis of three observational cohort studies including 1031 non-anemic CKD patients with eGFR <60 mL/min/1.73 m(2) regularly followed in renal clinics. We estimated the incidence of mild anemia (hemoglobin 11-12 g/dL in women and 11-13 g/dL in men) and severe anemia (hemoglobin <11 g/dL or use of erythropoiesis-stimulating agents) during a 3-year follow-up period. Thereafter we estimated the risk of end-stage kidney disease (ESKD) and all-cause death associated with new-onset mild and severe anemia. Results The mean age was 63 +/- 14 years, 60% were men and 20% had diabetes. The mean estimated glomerular filtration rate (eGFR) was 37 +/- 13 mL/min/1.73 m(2) and the median proteinuria was 0.4 g/day [interquartile range (IQR) 0.1-1.1]. The incidence of mild and severe anemia was 13.7/100 patients-year and 6.2/100 patients-year, respectively. Basal predictors of either mild or severe anemia were diabetes, lower hemoglobin, higher serum phosphate, eGFR 0.50 g/day. Male sex, moderate CKD (eGFR 30-44 mL/min/1.73 m(2)) and moderate proteinuria (0.15-0.50 g/day) predicted only mild anemia. The incidence of anemia increased progressively with CKD stages (from 8.77 to 76.59/100 patients-year) and the proteinuria category (from 13.99 to 25.02/100 patients-year). During a median follow-up of 3.1 years, 232 patients reached ESKD and 135 died. Compared with non-anemic patients, mild anemia was associated with a higher adjusted risk of ESKD {hazard ratio [HR] 1.42 [95% confidence interval (CI) 1.02-1.98]} and all-cause death [HR 1.55 (95% CI 1.04-2.32)]. Severe anemia was associated with an even higher risk of ESKD [HR 1.73 (95% CI 1.20-2.51)] and death [HR 1.83 (95% CI 1.05-3.19)]. Conclusions New-onset anemia is frequent, particularly in patients with more severe renal damage and in those with diabetes mellitus. The occurrence of anemia, even of a mild degree, is associated with mortality risk and faster progression towards ESKD.