GSTM1 and polycythemia: These variants may cause erythrocytosis (red cell mass greater than 125% above the expected value for sex and body mass) [2] and/or polycythemia (Hb > 16.5 g/dL − hematocrit (Hct) > 49% for men and Hb > 16.0 g/dL − Hct > 48% for women) [3].