“…This was handled by multiple imputations, which eliminates bias due to data not missing at random and increases external validity, but may compromises internal validity. Although our registry is nationwide it does not have complete coverage, and patients enrolled may be different than those not enrolled 153 . Moreover the hemoglobin level was obtained as a single measure at hospital discharge/clinical visit, therefore, we cannot clarify and quantify the changes in hemoglobin to verify how many patients were affected with transitory anemia or hem dilution and we do not know the true etiology of anemia since the pathogenesis is still unclear even if a number of underlying causes contributing to anemia have been suggested.…”