Figure 2: Pre/Postoperation Hb level category for risk of major complications. Preoperative Hb level and postoperative Hb level was stratified into different category. (a) In preoperative Hb level, both group (Hb <12.3 and 12.3 ≤Hb <13.8) had increased crude OR comparing with reference group (The definition is Hb greater is between 11.7 and 13.8), (b) In postoperative Hb level, only when Hb <10.3 had significant increased risk of free flap complication than reference group (Hb ≥11.7). OR: Odds ratio, Hb: Hemoglobin.