The critical relationship between cerebral blood flow and HbS levels in individuals with SCA. The study conducted by Hurlet-Jensen et al¹⁵  describes the unique relationship between hemoglobin (Hb) and HbS levels and CBF in individuals with SCA. As Hb levels increase, CBF decreases (r = −0.68, P = .006). As HbS levels increase, CBF increases (r = .080, P = .0003). In a stepwise multiple regression equation with Hb and HbS, only HbS was accepted and predictive of CBF (r = 0.70, P = .01). The figure depicts regression lines with 95% CI describing the relationship between Hb, HbS, and CBF. (A-B) Effect of total Hb and HbS on regional CBF measured by Xe inhalation: transfusion therapy.