Relationship between hemoglobin level and oxygen delivery in individuals with SCD. The maximal hemoglobin (Hb_max) to deliver oxygen transport in sickle cell patients is 10 to 11 g/dL because SCD alters red cell viscosity and decreases oxygen transport. However, when the HbS level is low (∼20%), this impairment of oxygen transport is improved, and a higher hemoglobin level (such as 13 g/dL) may be beneficial. Red cell apheresis can rapidly lower the HbS to levels that maximize oxygen delivery, in contrast to the risks of simple transfusion resulting in increased viscosity and decreased oxygen delivery.^82,83  Professional illustration by Patrick Lane, ScEYEnce Studios. Adapted from Swerdlow with permission.⁸⁰