Risk factors and external validation of nomogram model for patients with postoperative hemoglobin < 80 g/L after lumbar interbody fusion surgery

To identify risk factors for postoperative low hemoglobin (Hb < 80 g/L) after lumbar interbody fusion surgery and to externally validate an existing predictive nomogram developed by Xu Xiong et al. for estimating the risk of postoperative anaemia. A retrospective analysis was conducted on 830 patients who underwent lumbar interbody fusion surgery at a single tertiary centre. Postoperative outcomes across three Hb strata (< 70 g/L, 70–79 g/L, ≥ 80 g/L) were compared. Logistic regression was applied to identify independent predictors of postoperative Hb < 80 g/L. The nomogram was externally validated by assessing discrimination, calibration, precision-recall performance, threshold-dependent behaviour, and decision-curve utility. Lower postoperative Hb levels were associated with greater postoperative resource utilisation, including higher transfusion rates, increased wound drainage, and higher hospitalisation costs. Univariate analyses identified female sex, lower preoperative Hb levels, greater blood loss, higher intraoperative infusion volumes, and greater urine output as significant predictors. Multivariable regression demonstrated that lower preoperative Hb levels, posterior lumbar interbody fusion (PLIF) (vs. transforaminal lumbar interbody fusion (TLIF)), increased intraoperative blood loss, greater intraoperative infusion volume, and absence of hyperlipidemia independently predicted postoperative Hb < 80 g/L. Compared with the original model’s cohort, our patients exhibited higher BMI, lower preoperative Hb, higher platelet counts, significantly longer operative times, and substantially lower intraoperative blood loss—largely attributable to widespread adoption of minimally invasive/endoscopic TLIF (51.7%). External validation demonstrated moderate discrimination, with an AUC of 0.796. Sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) were 0.4667, 0.8318, 0.1373, and 0.9645, respectively. Calibration remained good, and decision-curve analysis indicated meaningful utility for ruling out low-risk patients. Postoperative anaemia after lumbar interbody fusion is influenced by preoperative hematologic status, surgical technique, and intraoperative management. The original nomogram showed limited PPV but retained good calibration and demonstrated its primary clinical utility in ruling out patients at low risk of postoperative hemoglobin < 80 g/L. Given the low event prevalence, lower probability thresholds may be more clinically suitable for screening purposes, whereas higher thresholds may support efficient exclusion of low-risk individuals. Thus, the model should be regarded primarily as a risk-exclusion and screening tool, rather than a definitive predictor of high-risk cases. Differences in surgical practice—particularly the high use of minimally invasive/endoscopic TLIF—significantly affected model transportability, highlighting the need for recalibration or development of updated prediction tools in larger, multicenter cohorts.