Guidelines for blood transfusion have been issued for years. According to these guidelines, red blood cells (RBCs) transfusion should be given when the hemoglobin level is less than 6g/dL or 7g/dL and is unnecessary when the level is more than 10g/dL. However, in all the guidelines, the determination of whether RBCs should be administered when the hemoglobin level is in the range of 6~10g/dL is based on the judgment from doctors. Index of transfusion trigger for patients with hemoglobin level between 6g/dL and 10g/dL is necessary and important in clinical practice.