Further comparison of total and hidden blood loss in patients undergoing single-level open and unilateral biportal endoscopic transforaminal lumbar interbody fusion

The primary objective of this study is to compare hidden blood loss (HBL) in patients undergoing single-level oblique transforaminal lumbar interbody fusion (O-TLIF) and unilateral lumbar interbody fusion (ULIF) using improved formula. The secondary objective is to evaluate and compare traditional versus improved methods for calculating HBL. A retrospective review was conducted on 30 patients who underwent ULIF and 33 patients who underwent O-TLIF between June 2023 and April 2025.For each group, the HBL was calculated by traditional and improved formula. The perioperative indicators, including TBL, HBL and measured blood loss (MBL), were compared. The data were analyzed using chi-square tests, analysis of covariance, parametric and non-parametric tests. Utilizing an improved formula, the ULIF group had significantly lower TBL and MBL (458.01 ± 249.39 ml, 60.21 ± 56.91 ml) than did the O-TLIF group (594.84 ± 254.44 ml, 219.80 ± 78.30 ml).The HBL was higher in the ULIF group (397.80 ± 260.52 ml) compared to the O-TLIF group (375.04 ± 245.44 ml), but this difference was not statistically significant ( p = 0.700).In the ULIF group, the HBL constituted 82.08 ± 19.91% of the TBL, whereas in the O-TLIF group, it accounted for 58.93 ± 17.05%. The ULIF group experienced reduced TBL, MBL compared to the O-TLIF group. Significant differences were observed in MBL, HBL, and HBL as a percentage of TBL in the TLIF group, and in MBL and HBL as a percentage of TBL in the ULIF group when comparing the traditional and improved formulas. Significant unmeasured blood loss frequently occurs in patients undergoing ULIF or O-TILF and should not be ignored. Compared with O-TLIF, ULIF is associated with a lower TBL and MBL. Compared to traditional and enhanced methods, improved formula represents a more effective strategy for estimating HBL.