Despite advances in patient blood management, the optimal hemoglobin threshold for Red Blood Cell (RBC) transfusion remains controversial. This observational study evaluated the association between the relative decline in Hematocrit (HCT) at the time of transfusion and postoperative outcomes in patients undergoing Coronary Artery Bypass Graft (CABG) surgery.

We conducted a retrospective cohort study of 629 patients who underwent CABG and received a transfusion at Tehran Heart Center Hospital, Iran, between March 2018 and December 2021. Based on the relative hematocrit reduction at the time of transfusion, patients were divided into two groups: Group A (≥ 40% change) and Group B (< 40% change). Early postoperative outcomes were compared between groups. Primary outcomes included mortality, hospital length of stay, intensive care unit length of stay, and intubation time. The composite secondary outcome comprised postoperative infection, renal failure, tamponade, and reoperation due to bleeding.

There were no significant differences in primary outcomes, except hospital length of stay (p = 0.02). However, after adjustment for potential confounders, this difference was no longer significant (p = 0.32). Composite secondary outcomes were comparable between the two groups, with no significant difference observed (p = 0.85).

In patients undergoing CABG surgery, this study did not identify a significant difference in early postoperative outcomes between two transfused patient groups stratified by a 40% change in HCT. Further prospective studies are needed to determine clinical relevance of relative hematocrit decline at the time of transfusion as a potential adjunct to conventional transfusion triggers.