GSTM1 and chronic obstructive pulmonary disease: According to the World Health Organization (WHO), anemia is defined as a hemoglobin (Hb) level of less than 13 g/dL in males and 12 g/dL in females [9]; however, it is debatable to what extent anemia is associated with adverse outcomes in critically ill COPD patients requiring invasive or non-invasive modes of ventilation and how it should be managed.