The promise of precision medicine includes understanding each person’s body on such a minute level that physicians can make even common procedures, such as blood transfusions, safer than ever before.
For a successful blood transfusion, donor and patient blood types must be matched accurately. Otherwise, the immune system attacks donor cells as invaders, causing shock, kidney failure, and even death.
At Cedars-Sinai, a new technique called extended blood matching goes beyond the standard typing of A, B, O, and AB, and positive or negative Rh factor. “We are one of very few hospital blood banks that uses genetics for blood typing and matching,” says Ellen Klapper, MD, director of Transfusion Medicine at Cedars-Sinai.
Matching a blood donor to a recipient comes down to antigens, which are encoded in our DNA. Blood types A and B, and the Rh factor, refer to antigens: proteins and sugars that sit on the surface of blood cells — which is all most hospital transfusion services test for. However, dozens of other antigens reside on red blood cells that, while harmless in the donor, can cause an immune reaction in the recipient.
As a result, up to 60 percent of transfusion recipients may experience an unintended immune response, depending on their health status and other factors. Patients receiving multiple transfusions, or who have conditions such as sickle cell disease, are at highest risk. In addition to the immediate health problems, antibody formation can complicate future transfusion therapy and increase the cost of treatment.
Klapper’s studies have been instrumental in demonstrating that a hospital transfusion service can test for genetically based variations in antigens. Previously, such molecular testing was restricted to specialized labs.
“We also showed that, in a hospital setting, it is quite possible to select more highly matched blood for transfusion, thereby reducing the risk of antibody formation — the immune response,” Klapper says.
The Cedars-Sinai blood bank has genetically typed 15,000 donors since 2008 and can now identify 32 antigens with a single blood test.
Klapper next plans a study to test Rh-negative blood donors because she believes some actually may be Rh-positive but carry an atypical protein.
“This is precision medicine,” Klapper says of the increasingly nuanced categories for typing patients. “We can’t put people in two large buckets of Rh-positive or Rh-negative anymore. The buckets are more like a variety of teacups.”