GSTM1 and polycythemia: While prospective, genotype-stratified trials with HIF-PHIs are still needed, these data motivate a personalized medicine framework in cardiorenal anemia syndrome: (i) consider TMPRSS6 (hepcidin) and selected HIF-pathway variants where available; (ii) pair initiation with closer Hb velocity and iron-index monitoring in genetically higher-risk profiles; and (iii) apply standard Hb action thresholds to prevent overshoot into polycythemia [107].