The SIT trial showed reduced recur- rent stroke in children with SCD and silent cerebral infarct who underwent transfusion compared with 2. SWiTCH (Stroke With Transfusions Changing to Hydroxyurea) was a randomized secondary stroke prevention trial in a pediatric SCD population that found no recurrent strokes with long-term trans- fusion but 10% with hydroxyurea.659 In situations in which transfusion is not available, a nonran- domized study of patients with an initial stroke suggested that patients who do not receive hydroxyurea have a higher recurrent stroke risk TWiTCH (TCD With Transfusions Changing to Hydroxyurea) was a primary stroke prevention randomized trial of children with SCD and abnormal TCD veloci- ties (>200 cm/s) but no severe vasculopathy who had received 1 year of transfu- sions. Children were subsequently randomized CLINICAL STATEMENTS AND GUIDELINES Kleindorfer to transfusion or hydroxyurea. Noninferiority was shown: 3 TIAs in each group and no new MRI stroke in either group. Hematopoietic cell trans- plantation can be curative for SCD662 but is usu- ally undertaken in children refractory to other treatment; it results in survival without SCD in 80% to 90% of patients. Clinical and subclini- cal infarctions have been reported to be arrested by this procedure.663 Surgical bypass has been reported with improved outcomes in patients with SCD with moyamoya, but no randomized data are Given the lack of experience with antithrombotics, antihypertensive agents, and statins for secondary stroke prevention in SCD, specific recommendations cannot be stated out- side of general treatment recommendations. Knowledge Gaps and Future Research Most studies for primary or secondary stroke preven- tion in SCD were conducted in the pediatric popu- lation. 