In usual practice, TKA is performed with a bloodless field using a tourniquet. Thus intraoperative blood loss can be negligible and postoperative drainage is only considered as VBLvisible. In terms of IBL, Sehat et al. found that TKA carried a substantial IBL. Their results shown the mean IBL was 765 ml or 49% of the mean total blood loss after TKA. Therefore, the true total blood loss was underestimated if not takes IBL into account.