Blood transfusion in sickle cell disease.

Sickle cell anemia is an inherited disease that causes chronic hemolytic anemia. Its pathognomonic signs and symptoms are caused by hemoglobin (Hb) S, which results from a single nucleotide substitution in the β-globin gene that places the amino acid valine with glutamic acid at codon 6 of the β-globin chain. Hb S is an insoluble Hb that crystalizes at low oxygen tension and other precipitating conditions leading to rigidity of red cells and clumping in small blood vessels. Patients with sickle cell disease have a variable Hb level that may range from 7.0 to 11.0 g/dL in their steady state condition. The most common cause of hospital presentation is due to acute painful crisis that results from vaso-occlusion by sickled cells. These episodes are treated with hydration and analgesia and do not require blood transfusion. Blood transfusion should be aimed to increase tissue delivery of oxygen. Hb S is known to be a low affinity Hb and so delivers oxygen at a lower partial pressure of oxygen compared to Hb A. Even with adequate pre transfusion testing and precautions, blood transfusion is never totally safe and short or long term complications may occur. Blood transfusion in patients with sickle cell disease has only limited indications such as acute hemolytic, aplastic or sequestration crises. Chronic transfusion protocols are implemented in cases of strokes or high cerebral blood flow ultrasonic studies as a prophylactic measure. Exchange blood transfusion is used in some complications of the disease such as acute chest syndrome (ACS), priapism or peri operatively. Once it is decided to transfuse blood, the transfused blood should be Hb S negative, Rh and Kell antigen matched.