BACKGROUND: This retrospective analysis was performed to investigate the potential influence of intra-operative blood transfusion (IBT) in patients aged 65 years or older with intertrochanteric fractures (IF) who underwent intramedullary fixation. METHODS: The outcomes of interest included the incidence of postoperative delirium (POD), pain score at discharge, length of hospital stay (LOS), functional outcomes, and mortality. The study included all surgically treated patients with IF between Jan. 2018 and Dec. 2021. Data on patient demographics, injury-related factors, surgical procedures, intraoperative details, in-hospital information, and postoperative outcomes were collected. In order to mitigate potential confounding and selection bias, the researchers employed the propensity score matching (PSM) technique using a 1:1 ratio via the caliper matching method. Following PSM, the association between IBT and outcome analyses was assessed using McNemar's Chi-square tests. Additionally, the Spearman correlations between IBT, POD and postoperative functional outcomes were computed. RESULTS: Out of the initial 2159 consecutive patients screened, a final sample of 1681 individuals was included, consisting of 1278 in the non-IBT group and 403 in the IBT group. After PSM, each group comprised 298 participants. The disparities in POD rate and functional outcomes became significant after employing propensity score-based matching (P <
0.002 and 0.029, respectively), despite their lack of significance prior to matching. There were no notable distinctions observed in other operation-related data, LOS, and crude mortality rates at 30-day, 90-day, and 12-month intervals before and after PSM. Furthermore, incidence of POD (P = 0.006) and functional outcomes (P = 0.013) were significantly associated with IBT. CONCLUSION: In conclusion, IBT significantly increases the incidence of POD and hinders postoperative functional recovery in elderly patients with hip fracture.