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Sickle Cell Disease Treatment–a Battle Against Alloimmunization

Sickle cell disease, or SCD, is an inherited, chronic group of disorders that affects hemoglobin, the molecule in red blood cells that delivers oxygen to cells throughout the body. It causes red blood cells, or RBCs, to be sickle-shaped and inflexible, rather than round and malleable. Normal RBCs carry oxygen, moving freely throughout blood vessels. Sickled RBCs stick together and get caught on blood vessel walls creating blockages, which can cause severe pain, (referred to as pain crises), chronic anemia, organ damage, stroke, infections and a life-threatening condition called acute chest syndrome.

People with SCD inherit two abnormal hemoglobin genes, one from each parent. SCD is most common in those with African ancestry, but is also seen in persons from Central or South America, Southeast Asia, the Middle East and the Mediterranean.

When an individual inherits one sickle hemoglobin gene and one gene for normal hemoglobin, they have sickle cell trait, or SCT. In the U.S., approximately one in 13 African Americans has SCT. These individuals have red blood cells that make both normal and sickle hemoglobin. People with SCT can have complications during intense physical activity or at high altitude, however most people with SCT do not have any medical complications. If both parents have SCT there is a 25 percent chance with every pregnancy that any child of theirs will have SCD. In the U.S., approximately one in 365 African American and one in 16,000 Latino babies are born with SCD, which is currently about 100,000 Americans.

Treatment of SCD involves infection prevention with antibiotics and immunizations, pain medications for pain crises and sometimes, use of a drug called hydroxyurea. Transfusions, which provide normal donor RBCs, are also an important part of SCD treatment. 

SCD patients who need RBCs transfusions may only need one or two units at a time. Many patients are also treated with a procedure called RBCs exchange, which removes blood containing sickle cells, replacing it with healthy RBCs from several units of donated blood. As with any blood transfusion, the donor RBCs must be matched to the recipient’s ABO blood type. However, there are hundreds of other molecules on RBCs, called antigens. For most patients non-ABO antigens do not cause transfusion problems. But, the SCD patient can develop an immune response to non-self RBCs antigens, called alloimmunization, creating a need for specially matched RBCs and even the inability to receive further transfusions.

According to Sally Campbell-Lee, M.D., Director, Centralized Transfusion Service for The Institute for Transfusion Medicine and Director, Transfusion Medicine at University of Illinois, Chicago, “Red blood cell alloimmunization occurs in approximately 30 percent of transfused sickle cell disease patients compared to two to five percent of all transfusion recipients.” This higher rate is mostly the result of differing “RBC antigen expression frequencies between the mostly Caucasian donor base and the mostly African American SCD patients, however other factors may contribute.” The National Institutes of Health reports that “nationally, minorities are underrepresented in community blood donation programs,” and that over 70 percent of donated blood is from Caucasian donors. Because of the differences in RBCs antigen expression between African Americans and Caucasians, specialized RBCs antigen matching for SCD patients requires blood donations from African American donors.

Dr. Campbell-Lee stated, “specialized selection of RBCs for SCD patients have become more widely used in order to prevent RBCs alloimmunization.” Results of several studies utilizing these special matching protocols revealed the alloimmunization rate was lowered to about eight percent.

The Sickle Cell Center at UIH serves a large population of pediatric and adult patients in the Chicago region. The UIH Transfusion Service, under Dr. Campbell’s leadership, performs chronic and episodic RBCs transfusions including RBCs exchange. She stated, “There are 50 patients in the chronic RBCs exchange program at UIH. A patient may need between five and 10 units of RBCs each month. Each of these patients receives prophylactic antigen matching of their RBCs units (underscoring the need for more African American donors in support of SCD patients.)”  

Full PubMed.gov article:

Red Blood Cell Alloimmunization in Sickle Cell Disease: Listen to Your Ancestors

NIH National Heart, Lung and Blood Institute page explains types
of
sickle cell disease.

© The Institute for Transfusion Medicine