Relationship between hemoglobin, hemolysis, and transcranial Doppler velocities in children with sickle cell disease: Results from a long-term natural history study in Italy in the era of multimodal therapy

Background: Stroke and cerebral vasculopathy are leading causes of morbidity and mortality in patients with sickle cell disease (SCD). Transcranial Doppler (TCD) is a reliable and validated predictor of stroke risk. Children with conditional or abnormal TCD are at an increased risk for stroke, which can be mitigated by red blood cell transfusion or hydroxyurea. Elucidating the relationship between cerebral hemodynamics and hemolytic anemia can help identify novel therapeutic approaches to reduce stroke risk and transfusion dependence.Methods: This long-term, real-world study was designed to evaluate the prevalence of TCD imaging (TCDi)-assessed flow velocities in children and to interrogate their relationship with markers of anemia and hemolysis.Results: In total, 155 children (median follow-up 79.8 months, 1358.44 patient-years) had 583 evaluable TCDi results. Only patients with HbSS or HbS beta(0) had abnormal (1.6%) or conditional (10.9%) TCDi. Children with abnormal or conditional TCDi had lower hemoglobin (Hb) and higher hemolysis markers. A linear correlation was detected between TCD velocity and Hb: an Hb increase of 1 g/dL corresponded to decreases in velocity in the internal carotid and middle cerebral arteries (6.137 cm/s and 7.243 cm/s). Moreover, patients with Hb >9 g/dL presented a lower risk of TCDi-associated events.Conclusion: These results support the need to optimize disease-modifying treatments that increase Hb and reduce hemolysis for stroke prevention in young children with SCD.