In-hospital morbidity and mortality rates according to the number of erythrocyte units transfused. In-hospital morbidity (a composite of all five morbid events shown in fig. 2) increased with erythrocyte dose in a curvilinear manner, reaching a 50% rate of morbidity at 10 or greater erythrocyte units. The slope was steepest up to 30 erythrocyte units, with an inflection point and plateau at higher doses. The formula defining the curve is y = 36.5 ln(x) + 10.4 (R² = 0.962). Mortality increased in a linear manner with a slope close to 10, indicating that for each 10-erythrocyte unit increment, mortality increased approximately 10%. After transfusion of 50 units, mortality exceeded 50%. The formula defining the curve is y = 9.47 (x) − 10.56 (R² = 0.99). RBC = erythrocyte.