Wen L, et al. - Researchers assessed the hidden blood loss (HBL) of patients who underwent lumbar fusion surgery for degenerative spine and evaluated its risk factors. Among these patients who underwent posterior lumbar fusion surgery for degenerative spine, 588 mL was the mean amount of HBL, which was 39% of blood loss. Also, a probable correlation of significant hidden loss with postoperative mortality was seen. When considering strategies of fluid infusion and blood transfusion, multilevel fusion, surgical time, and fibrinogen level ought to be paid close attention.