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About 30% of transplant patients are sensitized. This means that they have harmful antibodies which will attack foreign tissue, such as the transplanted organ from a living donor. These antibodies develop through a previous exposure to foreign tissue, such as through pregnancy, previous transplants, or blood transfusions. Sensitized patients may wait three to four times longer than unsensitized patients for a compatible deceased donor kidney.
To test a recipient for these antibodies, a sample of their blood is mixed with a sample of the potential donor’s blood. This test is called a “crossmatch,” and shows how a recipient’s antibodies react with the potential donor’s.
Test results can be either positive or negative. It may seem confusing at first, but a positive crossmatch means that a donor and recipient are not compatible.
Positive crossmatch ⇒ Recipient’s antibodies attack donor’s ⇒ Not suitable for transplantNegative crossmatch ⇒ Recipient’s antibodies do not attack donor’s ⇒ Suitable for transplant
If a donor and recipient are not compatible, a transplant can still be performed. Experts at the Johns Hopkins Comprehensive Transplant Center developed a method call plasmapheresis, which helps make a kidney more compatible for a recipient and significantly affects survival outcomes.