GSTM1 and chronic kidney disease: LVEF: Left ventricular ejection fraction; NYHA: New York Heart Association; Hb: Hemoglobin; HF: Heart failure; TSAT: Transferrin saturation; CrCl: Creatinine clearance; CRP: C-reactive protein; 6MWT: 6-minute walk test; MLHFQ: Minnesota living with heart failure questionnaire; pVO2: Normal mixed venous oxygen tension; PGA: Patient global assessment; KCCQ:  Kansas City cardiomyopathy questionnaire; EQ-5D: European quality of life 5D; CKD: Chronic kidney disease; QoL: Quality of life questionnaire; VAS: Visual analogue scale; CV: Cardiovascular death