GSTM1 and anemia (phenotype): 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.