GSTM1 and chronic obstructive pulmonary disease: Erythrocytosis as a complication of COPD is diagnosed following findings of haemoglobin (Hb) concentration of Hb > 16.5 g/dl or hematocrit (HCT) > 49% in males and Hb > 16 g/dl or HCT > 48% in females [12].