This divergence in Δ[Hb]/altitude indicates profound problems in the diagnosis of anemia and polycythemia in high-altitude residents because until now their diagnosis was based on a single algorithm for altitude adjustment of [Hb] as presented by the WHO for world region-unspecific, and age-independent use.12 These discrepancies need to be overcome by re-defining altitude-dependent normal [Hb] ranges. Here, GSTM1 is linked to anemia (phenotype).