GSTM1 and chronic kidney disease: Taking group 1 (“lower and decreasing”; Hb<100 g/L, HCT approximately 30%) as reference, group 2 (“lower and growing slightly”; Hb 110–120 g/L, HCT approximately 35%), group 3 (“higher and growing slightly”; Hb 125–135 g/L, HCT approximately 40%), and group 4 (“higher and growing steadily”; Hb 145–160 g/L, HCT approximately 45%) were independent protective factors for the occurrence of the composite outcome in patients with CKD stages 3–4 (p=0.