Preoperative anemia is present in more than 50% of patients undergoing cardiac surgery, which is associated with increased risk of transfusion, increased length of stay in the intensive care unit, and increased incidence of renal failure and mortality.

To date, clinical research on perioperative anemia has been focused on finding and treating other underlying causes of anemia, lowering the threshold for transfusion, and performing careful transfusion.

However, recently, it was known that hepcidin and erythroferrone are related to iron metabolism and absorption, vitamin D has an inverse correlation with the development of anemia, and is related to hepcidin concentration control.

Therefore, in this study, the relationship between vitamin D, hepcidin concentration and perioperative hemoglobin level in patients with off-pump coronary artery bypass graft surgery was investigated together.

Inclusion Criteria:

1. Patients over 20 years of age undergoing off-pump coronary artery bypass graft

Exclusion Criteria:

1. Emergency operation
2. Minimal invasive coronary artery bypass graft
3. Cooperative operation with other surgery
4. Patients who need a mechanical ventricular assist device
5. Patients with chronic kidney disease (eGFR < 30)
6. Patients who have a end stage renal disease and need a hemodialysis
7. Patients with a low hemoglobin (Hb < 10) before surgery
8. Patients who have a some disease(leukemia, myeloma, aplastic anemia, sickle cell anemia, etc) affecting hematopoiesis
9. Patients with a liver cirrhosis
10. Patients who receive vit. D, iron supplements, erythropoietin within 6 months
11. Patients who cannot understand the informed consent (eg. Foreigner, patients with cognitive dysfunction, etc)
12. Patients who disagree this study

Patients who consented to study enrollment among patients scheduled for off-pump coronary artery bypass graft