We studied the association between Hb level and iron indexes combining 2 or 3 of the following markers: serum ferritin (<40 ng/mL), transferrin saturation (TSAT<20%) and total iron binding capacity (TIBC<50 μmol/L) in 1011 outpatients with non-dialysis CKD participating in the Nephrotest study. The gene discussed is GSTM1; the disease is chronic kidney disease.