Table 1 Estimations of Perioperative Blood Loss Volume

Orthopedic Surgery Transfusion Hemoglobin European Overview (OSTHEO) formula:

① Estimated blood volume (EBV) = (0.0235 × height in cm^0.42246 × weight in kg^0.51456) × k, where k = 2430 for women and 2530 for men.

② Total RBC loss (mL) = [Uncompensated RBC loss (mL) + Compensated RBC loss (mL)]/0.35

Uncompensated RBC loss (mL) = EBV × (preoperative Hct levels − postoperative Hct levels),

Compensated RBC loss (mL) = allogeneic erythrocyte units ×  150 + autologous transfusion volume ×  0.3.

Notably, postoperative Hct levels were collected from the laboratory test which was carried out on the 1st, 3rd, and 5th day after operation. Only transfusions that were executed before phlebotomizing for laboratory test were included in the study.