Abstract:To evaluate the influence of obesity on perioperative blood loss following enhanced recovery after primary total knee arthroplasty (TKA). Methods The patients undergoing primary TKA were divided into normal group (BMI: 18.0 to 24.0 kg/m2), overweight group (24.0 to 28.0 kg/m2) and obese group (BMI ≥ 28.0 kg/m2) according to body mass index (BMI) from August 2017 to August 2018. We evaluated the baseline indicators, total blood loss (TBL), intraoperative blood loss, hidden blood loss (HBL), the ratio of TBL and patient’s blood volume (PBV), transfusion rate, hemoglobin and hematocrit drop, length of hospital and incidence of complications. Results The PBV was the most in obese patients (P?0.05). The TBL and HBL in obese group were higher than those in normal and overweight group (P?0.05). There was no significant difference in the intraoperative blood loss, ratio of total blood loss and PBV, hemoglobin or hematocrit drop among the three groups (P?>?0.05). No transfusion, pulmonary embolism and deep infection was emerged. The incidences of deep vein thrombosis, incision swelling and exudation, nausea and vomiting were similar (P?>?0.05). Conclusion Obese patients suffered from higher risk of perioperative blood loss, especially HBL following enhanced recovery after primary TKA. However, the ratio of TBL and PBV, allogeneic transfusion rate, the changes of hemoglobin and hematocrit are similar among the three groups.