Kidney transplantation offers a life-altering treatment for individuals with end-stage renal disease. For those considering a living donation, compatibility is a complex biological measure of how the recipient’s immune system will react to the new organ. While living donation improves success rates and reduces wait times, the question of whether a donor must have the same blood type remains common. The answer is not a simple yes or no, as medical advancements allow for successful transplantation even when a direct biological mismatch exists.
Required Blood Type Matching
Historically, a direct match between the donor’s and recipient’s ABO blood groups was mandatory to prevent immediate rejection. This necessity stems from natural antibodies in the recipient’s bloodstream that target antigens found on different blood types. For instance, a person with Type A blood has anti-B antibodies, which would instantly attack a Type B donor kidney.
The standard compatibility rules dictate that Type O individuals are “universal donors” because their kidneys can be accepted by any other blood type. However, they can only receive organs from other Type O donors. Conversely, Type AB recipients are “universal recipients” as they possess neither anti-A nor anti-B antibodies and can receive a kidney from any ABO type.
The Rh factor (positive or negative) is not a relevant barrier in kidney transplantation. Unlike blood transfusions, the Rh antigen is present only on red blood cells and not on the kidney tissue itself. For a successful transplant, the focus remains on the ABO group and other immune markers.
Compatibility Factors Beyond ABO
Even when blood types are compatible, the immune system uses other mechanisms to identify foreign tissue, requiring further testing to predict rejection risk. The most significant mechanism involves Human Leukocyte Antigens (HLA), which are proteins found on the surface of most cells. These HLA markers allow the immune system to distinguish the body’s own cells from foreign cells.
Every person inherits three HLA markers (A, B, and DR) from each parent, resulting in six primary markers assessed for transplantation. The goal of HLA typing is to find a donor-recipient pair with the lowest number of mismatches. A closer match correlates with better long-term graft survival, and a low mismatch score indicates a lower immunological risk.
The final test of immediate compatibility is the Crossmatch test, performed by mixing the recipient’s serum with the donor’s lymphocytes. If the recipient’s pre-existing antibodies attack the donor cells, the result is a “positive crossmatch.” This historically meant the transplant could not proceed due to the high risk of hyperacute rejection, while a “negative crossmatch” clears the way for surgery.
Options for Incompatible Donations
When a willing living donor and a recipient are incompatible, either due to blood type or a positive crossmatch result, two primary medical strategies are used to proceed with the donation. The most common solution is Kidney Paired Exchange (KPE), also known as a kidney swap.
Kidney Paired Exchange (KPE)
KPE involves finding another incompatible donor-recipient pair and arranging a “swap” where each donor gives a kidney to the other pair’s compatible recipient. KPE systems use a centralized database to match pairs based on compatibility factors. This allows the original donor to help their loved one receive a kidney while donating to a stranger. KPE has become the solution for the majority of ABO-incompatible pairs. In some cases, a chain can be started by an altruistic, non-directed donor, allowing multiple pairs to receive compatible transplants.
Desensitization Protocols
For cases that cannot be resolved through KPE, or for recipients with high levels of pre-existing antibodies, a direct incompatible transplant can be performed using Desensitization Protocols. These protocols involve intensive medical treatments before and after the surgery to lower the level of harmful antibodies in the recipient’s bloodstream. Treatment often includes plasmapheresis, a procedure that removes the recipient’s plasma containing the antibodies and replaces it with a substitute. Medications like rituximab are also used to suppress the immune cells that produce the antibodies. The goal is to reduce antibody levels below a safe threshold to prevent immediate rejection.