GSTM1 and anemia: WHO's approach to correcting the Hb distribution curve for altitude increases the proportion of subjects classified with anemia while reducing the proportion with Hb > 14.5 g/dL or excessive erythrocytosis (i.e., Hb levels above 21 g/dL in men and 19 g/dL in women [54]), which may diminish potential adverse health implications of high Hb levels [55].