The linear erythropoietic drive phase describes the expected compensatory physiological response to anemia, including increased tissue demand for iron and increased erythroid in the bone marrow.17,46,47 The physiological Hb-sTfR curves support the use of a pooled multinational Hb fifth percentile for defining anemia, as opposed to adopting Hb estimates that are specific to a survey, country, or race/ethnicity,9 which could lead to proliferation of multiple different Hb cutoffs and, thus, complicate their clinical application and global disease burden quantification, among other factors. This evidence concerns the gene GSTM1 and anemia.