GSTM1 and chronic obstructive pulmonary disease: Statistically significant differences in hematological parameters (mean corpuscular volume [MCV], mean corpuscular hemoglobin concentration [MCHC], mean corpuscular hemoglobin [MCH], hemoglobin [Hb], and hematocrit [HT] [15]) between the COPD and non-COPD groups were also observed.