Timing of intravenous iron for treatment of anaemia in surgical patients: a systematic review and network meta-analysis.

Background: Anaemia complicates recovery in surgical patients. Intravenous (IV) iron supplementation shows promise in improving outcomes, but optimal timing remains uncertain. In this review, we compare the efficacy, safety, tolerability, and outcomes between preoperative and postoperative IV iron supplementation. Methods: In this systematic review and network meta-analysis, we searched PubMed, EMBASE, Cochrane Library, and Web of Science from inception to May 1, 2025, for randomised controlled trials (RCT) investigating IV iron supplementation in surgical patients either 7-30 days before surgery (preoperative) or 0-30 days after surgery (postoperative). Studies were excluded if they included patients with critical illness or prior transfusion or if iron was given outside the defined time frames or with other agents. Two reviewers independently appraised the data and extracted summary estimates from published reports. The primary outcomes were: (1) proportion of patients who received blood transfusion; (2) change between the baseline haemoglobin level and the haemoglobin level on postoperative day (POD) 7 and POD30. Data processing was conducted based on frequentist network meta-analysis. The risk of bias was assessed using the Cochrane Risk of Bias tool. The protocol is registered with PROSPERO, CRD42024533265. Findings: Among 129 identified studies, 22 RCTs with 3026 patients were included. All included studies had a low (n = 6) or moderate (n = 16) risk of bias. Compared to controls, postoperative IV iron supplementation reduced transfusion rates (RR 0.80, 95% CI 0.68-0.94; I Interpretation: Our results suggest that postoperative IV iron supplementation reduces transfusion rates, while preoperative supplementation improves haemoglobin recovery. Clinicians may choose either strategy in an individualised, patient-centered manner. These conclusions should be interpreted with caution due to heterogeneity among included studies, limited data for subgroup analyses, and the absence of direct comparisons between preoperative and postoperative approaches. Funding: National Key Research and Development Program of China, National Natural Science Foundation of China, Beijing Natural Science Foundation, Capital's Funds for Health Improvement and Research, National High Level Hospital Clinical Research Funding, and Chinese Academy of Medical Sciences Innovation Fund for Medical Sciences.