GSTM1 and chronic kidney disease: Comparison between oral and intravenous iron has been better studied in a systematic review and meta-analysis in patients with chronic kidney disease [21], which showed that patients treated with intravenous iron were more likely to reach an Hb response > 1 g/dL (risk ratios (RRs) of 1.61 (95% CI, 1.39–1.87) for chronic kidney disease stages 3–5, and 2.14 (95% CI, 1.68–2.72) for CKD stage 5D).