BACKGROUND: Among patients subjected to massive transfusion (MT), some will require considerably more blood than others, depending on the rate and quantity of hemorrhage. In analyses concerning plasma to red blood cell (RBC) ratios and platelet to RBC ratios, this has yet to be examined.We sought to evaluate the effect of the number of RBC units transfused on both plasma:RBC and platelet:RBC and their association with mortality in MT patients. METHODS: Prospective datawere collected on trauma patients taken directly to surgery from the resuscitation roomwho received ≥10 RBC units by completion of operation. MT protocolwas in place for all patients. To account for survival bias, intra-operative deaths were excluded. Patients were stratified by plasma:RBC and platelet:RBC (HIGH > 0.5, MID 0.33-0.5, LOW < 0.33). Crude and adjusted risk ratios (RRs) for hospital mortality were determined, using the HIGH ratio as the reference group. RESULTS: One hundred thirty-five patients met inclusion criteria. There were no significant differences with respect to demographics, injury characteristics, or shock severity. However, the mean number of intra-operative RBC units transfused was significantly different between plasma:RBC groups (HIGH: 16.2, MID: 19.7, LOW: 25.1; p < 0.001). The crude risk for mortality was significantly higher for the LOW group relative to the HIGH group (RR 1.99, 95% confidence interval [CI] 1.02-3.89). However, after adjustment for the number of RBCs transfused, the risk was not significantly different (RR 1.54, 95% CI 0.75-3.15). The adjusted mortality risk for the LOW versus HIGH platelet:RBC groups was also not statistically different (RR 1.92, 95% CI 0.99-3.71). CONCLUSIONS: Among patients subjected to MT, those who receive relatively higher quantities of RBCs are both more likely to receive a lower plasma:RBC and are more likely to die. Any analysis concerning transfusion ratios should take the potential confounding of this heterogeneity among MT patients into account. Copyright © 2012 by Lippincott Williams & Wilkins.