Indications for blood transfusion in adults with SCD. Blood transfusion is increasingly used as a disease-modifying therapy in a number of acute and chronic complications, the majority of which have low to moderate quality or no evidence base. The highest-quality evidence is from randomized controlled trials on primary prevention of stroke in children.^52,53  Transfusion increases the Hb level and, therefore, the oxygen-carrying capacity, and it decreases the proportion of HbS in the circulation. Because sickled red blood cells increase viscosity, it is recommended that transfusion should not exceed a threshold of 10 g/dL.²⁹  It provides effective treatment of many of the complications of SCD. The list here is not exhaustive; a frequent use of blood transfusion is for symptomatic anemia in VOC when Hb falls below 20% of baseline, which again is not evidence based. Details of when and how to transfuse in SCD has been reviewed in ASH Education 2016.³²  Transfusion can be Simple (S) or Exchange (E) blood transfusion. Note: acute splenic sequestration is common and life threatening, and it can be recurrent; if so, consideration should be given to splenectomy. In progressive organ failure (cardiac, renal, and pulmonary), chronic transfusion can be considered an alternative when there is no response to HU or when HU cannot be used. DHTR, delayed hemolytic transfusion reaction; HPV-B19, human parvovirus B19; SCI, silent cerebral infarction; VOC, vasoocclusive crisis.