The prevalence of anemia (Hb level <12 g/dL in men and <11 g/dL in women) showed an increase from 1% (95% confidence interval [CI], 0.7%–2%) at GFR of 60 mL/min/1.73 m2 to 9% (95% CI, 4%–19%) at GFR of 30 mL/min/1.73 m2. This evidence concerns the gene GSTM1 and anemia.