Transfusion of red blood cells (RBCs) is a cornerstone of treatment to prevent the complications of sickle cell disease (SCD). SCD is caused by a mutation of the β-globin gene, resulting in glutamic acid being substituted by valine at position 6. The mutation results in an abnormal hemoglobin (Hb SS) that aggregates into a rigid sickle-shape under certain conditions. Individuals with SCD frequently require transfusion of RBCs to treat acute pain crisis (i.e. acute chest syndrome) and prevent chronic complications (i.e. stroke). RBC transfusion helps SCD patients by providing RBCs with hemoglobin A thus decreasing the amount of HbSS RBCs that can sickle and contribute to pain crisis and chronic complications. Unfortunately, alloimmunization to non-ABO RBC antigens is a potential complication of any patient receiving chronic transfusion therapy. The most life-threatening consequence of alloimmunization in SCD is the development of a delayed hemolytic transfusion reaction with hyperhemolysis. Alloimmunization also puts SCD patients at increased risk of receiving an incompatible transfusion due to difficulty in finding compatible blood and increases costs for the health care system.
Antigen matching beyond standard ABO and Rh typing can help reduce the alloimmunization rate in chronically transfused patients. A widely accepted antigen matching strategy used by transfusion services is to initially provide Rh and Kell-matched RBC units to SCD patients, even if the patient has not yet made an alloantibody (i.e. antibody screen negative) since the Rh (D, C, c, E and e) and Kell (K) antigens are among the most immunogenic. Providing Rh and K-matched RBC units continues until the patient proves to be an antibody former (i.e. anti-Jk(b)), after which the transfusion service provides fully phenotype matched RBCs for non-emergent transfusion when available. A “full” phenotype usually includes Rh, K, Jk(a), Jk(b), Fy(a), Fy(b), M, N, S and s.
In summary, the strategy for patients with SCD is as follows:
- Determine the patient’s full RBC phenotype (D, C, c, E, e, K, Kidd, Duffy, M, N, S, s) before transfusions begin. If transfusions already started, consider molecular testing.
- Provide Rh (D, C, c, E, e) and K-matched RBCs until the patient proves to be an antibody former.
- If the patient proves to be an antibody former, provide full phenotype matched RBC units to attempt to prevent any additional antibody formation and it becomes increasingly impossible to find compatible units.
-Thomas S. Rogers, DO is a second-year resident at the University of Vermont Medical Center, a clinical instructor at the University of Vermont College of Medicine, and the assistant medical director of the Blood Bank and Transfusion Medicine service.