Wang JQ, Guo WJ, Zhao YM, et al. - The present study was conducted to ascertain the amount of hidden blood loss after intramedullary nail fixation for extra-articular tibial fractures, meanwhile, identified the influential factors causing hidden blood loss (HBL). In this retrospective cohort study, 122 consecutive extra-articular tibial fracture patients fixed with intramedullary nail (IMN) and 96 met all inclusion criteria for the chosen analysis Between January 2015 and December 2017. Researcher assessed preoperative hematocrit (Hct) levels on admission and postoperative Hct levels on the third day after surgery to estimate the amount of HBL. A significant amount of postoperative HBL was found after IMN fixation of extra-articular tibial fractures. The results considered that surgeons should be aware that more HBL can be developed in patients who have male gender, small medullary cavity, and long-time surgical duration. The evidence revealed that for extra-articular tibial fractures, HBL deserves attention to ensure patients’ safety in the perioperative period of IMN fixation.