EPO and anemia (phenotype): For future optimal preoperative management of red blood cells in line with the guidelines and available data [28, 29] we need to elucidate reasons for preoperative anemia (e.g. iron deficiency, vitamin D or folate deficiency) and implement erythropoietin (EPO) treatment with or without iron supplementation (class IIa, level B recommendation) in our subsequent work.