Kidney transplantation offers a life-altering treatment for individuals living with end-stage renal disease. Ensuring compatibility between a donor and recipient is fundamental to promoting positive outcomes and mitigating the risk of the recipient’s immune system rejecting the new organ.
Blood Type Requirements
One of the initial and most straightforward compatibility factors is the ABO blood group system. Similar to blood transfusions, the donor and recipient must have compatible blood types to prevent an immediate, severe immune reaction against the transplanted kidney. For instance, a person with blood type A can receive a kidney from a donor with blood type A or O.
Blood type O is considered a universal donor, meaning individuals with this blood type can donate a kidney to recipients with A, B, AB, or O blood types. Conversely, recipients with AB blood are universal recipients, capable of receiving a kidney from any ABO blood type (A, B, AB, or O). While direct matches (e.g., A to A, B to B) are ideal, the main goal is preventing the recipient’s immune system from reacting against the donor’s blood type.
Tissue Type Compatibility
Beyond blood type, a more intricate level of matching involves human leukocyte antigens (HLAs), which are proteins found on the surface of most cells in the body. The immune system uses these HLA markers to distinguish between the body’s own cells and foreign invaders. A closer HLA match between donor and recipient reduces the likelihood of the recipient’s immune system mounting an attack against the transplanted kidney.
There are several main HLA markers, including HLA-A, HLA-B, and HLA-DR, that are particularly relevant in kidney transplantation. Each person inherits three HLA markers from each parent, resulting in six primary markers. While a perfect six-antigen match is uncommon, a greater number of shared HLA antigens leads to a lower risk of rejection.
The Crossmatch Test
A final and crucial compatibility check performed just before a kidney transplant is the crossmatch test. This test involves mixing a sample of the recipient’s blood serum with cells from the potential donor. Its purpose is to determine if the recipient has pre-formed antibodies that would immediately recognize and attack the donor’s kidney.
A “negative” crossmatch result indicates that the recipient does not possess such antibodies, allowing the transplant to proceed. Conversely, a “positive” crossmatch means that the recipient’s antibodies would react against the donor’s cells, signifying a high risk of hyperacute rejection and typically preventing the transplant from occurring.
Overall Health Assessment
Beyond specific blood and tissue compatibility, a comprehensive overall health assessment of the potential donor is important. This evaluation ensures the donor’s safety during and after the donation process and minimizes risks to the recipient. Donors undergo extensive screening for infectious diseases, including HIV and various forms of hepatitis.
Uncontrolled chronic conditions in the donor, such as diabetes, high blood pressure, or significant heart disease, typically preclude donation due to the potential for complications. Screening for active cancers is performed to prevent disease transmission to the recipient. A stable mental health evaluation is also conducted to ensure the donor is fully prepared for the donation journey.
Navigating Mismatched Donors
Even when a direct match based on blood type or HLA is not found, options exist for many patients awaiting a kidney transplant. Paired kidney exchange programs offer a solution for incompatible donor-recipient pairs. In these programs, two or more incompatible pairs swap kidneys, allowing each recipient to receive a compatible organ from another donor within the exchange.
These “kidney swaps” can involve two pairs or even larger chains, enabling transplants that would otherwise not be possible. Another approach for recipients with some antibodies against a donor is desensitization. This involves medical treatments, such as plasmapheresis and intravenous immunoglobulin (IVIg), to reduce the level of harmful antibodies in the recipient’s blood before the transplant, making a less-than-perfect match viable.