GSTM1 and chronic obstructive pulmonary disease: The results of this study showed that the guidelines regarding the upper reference limit for Hb in the COPD population with CKD were similar to those in the CKD population, suggesting that management of anemia for CKD patients may serve as a reference for the treatment of COPD complicated with CKD and that the upper reference limit for Hb should also be taken into consideration.