Red blood cell mass as a predictor of transfusion risk of packed red blood cells in cardiac surgery patients requiring cardiopulmonary bypass.

Introduction: Red blood cell (RBC) transfusion in cardiac surgery is associated with adverse outcomes and increased costs. Traditional predictors such as hemoglobin and BMI offer limited physiologic insight. This study evaluates RBC mass, a calculated measure of total red cell volume, as a preoperative predictor of transfusion in adult cardiac surgery patients undergoing cardiopulmonary bypass (CPB). Materials and Methods: This retrospective observational study included 463 adult patients undergoing elective cardiac surgery with CPB at a single academic center in 2024. Exclusion criteria included procedures with inherently high transfusion risk (e.g., redo sternotomy, LVAD implantation, circulatory arrest, and "bring-backs"). RBC mass was calculated using estimated blood volume (sex-adjusted mL/kg) and hematocrit. Patients were categorized into three RBC mass groups: 1-2 L, 2-3 L, and >3 L. Multivariable logistic regression was used to assess the association between RBC mass and transfusion, adjusting for sex, age, BMI, and bypass time. Results: Of the 463 patients, 102 (22 %) received RBC transfusions. Transfused patients had significantly lower RBC mass (mean 1.95 L) versus non-transfused (2.58 L, Discussion: RBC mass proved a more physiologically integrated and predictive metric for transfusion risk than hemoglobin or BMI alone. It may be especially useful in identifying at-risk female patients and those with normal hemoglobin but limited oxygen-carrying reserve. Conclusions: Preoperative RBC mass is a strong independent predictor of transfusion in cardiac surgery. Its incorporation into preoperative planning may improve patient optimization and reduce unnecessary transfusions.