Xu L, Chen Y, Xie Z, et al. - In this retrospective, multicenter population-based study, researchers examined the link between elevated hemoglobin (Hb) and in-hospital death and investigated reference Hb intervals in patients with chronic obstructive pulmonary disease (COPD) and chronic kidney disease (CKD). Participants were 47,209 in total. They used the average Hb level during hospitalization as the Hb level. They defined CKD as estimated glomerular filtration rate < 60 ml/min/1.73 m² and advanced CKD as estimated glomerular filtration rate < 30 ml/min/1.73 m². Using different multivariable logistic regression models, they examined the link between Hb level (measured in 1 g/dL intervals) and in-hospital mortality by CKD stratification. They found an increased risk of in-hospital mortality in relation to high Hb in COPD patients with CKD, particularly among those with advanced CKD. In this group of patients, those with high Hb levels deserve attention.