Limitations of the current study include lack of laboratory data; somewhat arbitrary definitions of hyporesponsiveness based on the ninetieth percentile of total monthly EPO dose, dose/kg, or dose/hemoglobin level; possible misclassification of comorbid conditions due to use of claims to identify them; lack of data on catheter use, which is known to be associated with increased risk of infection and inflammation; and residual confounding, which may explain some of the adjusted logistic regression findings. Here, EPO is linked to infection.