GSTM1 and chronic obstructive pulmonary disease: On the other hand, the prognostic value of an improved nutritional status has been demonstrated in severe COPD to be mainly related to the increase in BMI and other related indices [31]: BMI values proved directly related to Hb values in our population during LTOT, particularly in the anemic subgroup during the third year of the survey (Figures 4 and 5), thus emphasizing the possible role of LTOT in ameliorating the nutritional status (Hb included) of anemic subjects.