In turn, in patients with anemia on ESA treatment, Hb levels should be measured when clinically indicated—in the correction phase once in a month and in the maintenance phase: at least every 3 months in patients with CKD (not on dialysis), monthly in patients with CKD-5D (hemodialysis), and every 2 months in patients with CKD patients on peritoneal dialysis [42]. The gene discussed is GSTM1; the disease is anemia (phenotype).