Recipient Matching

Overview

For directed donation to work, your blood and tissue have to be a fit with your intended recipient's. Blood type is the most important factor. The recipient's immune system has to be able to accept the new organ without attacking it.

If you are not a natural match, options still exist. Paired exchange programs match you with another mismatched pair so you can trade organs. When tissue antibodies are the issue, desensitization treatment can sometimes let the transplant go forward. The team will tell you which options apply and walk through what each one looks like.

How compatibility works

How matching works

Living transplantation depends on preventing rejection. Your immune system recognizes your organ as "yours" because of proteins on the surface of your cells. The recipient's immune system must be unable to recognize your organ as "foreign," or must be suppressed enough to tolerate it.

Matching focuses on three main factors:

• Blood type (ABO system): Do your blood types allow transplantation?
• HLA (tissue type): How well do your tissue types match?
• Crossmatch: Are there antibodies in the recipient's blood that will immediately attack your organ?

All three matter, but blood type is the most critical baseline. You can transplant across HLA mismatch. You can sometimes transplant across crossmatch with special protocols. But blood type incompatibility has historically been an absolute barrier.

Blood type compatibility

Your blood type is determined by antigens on your red blood cells. The main ABO system has four types: O, A, B, and AB.

Compatible pairs

Some blood type combinations allow direct transplantation:

• O donors can give to O, A, B, and AB recipients (universal donors)
• A donors can give to A and AB recipients
• B donors can give to B and AB recipients
• AB donors can only give to AB recipients (but can receive from anyone)

If you fall into a compatible pair with your intended recipient, transplantation can proceed (assuming other tests are normal).

Incompatible pairs

If you and your intended recipient have incompatible blood types, direct transplantation isn't possible—unless you pursue special protocols. Some examples of incompatible combinations include O donors with B or A recipients, A donors with B recipients, and B donors with A recipients.

Incompatible blood type pairs cannot proceed directly:

• O donor cannot give to B or A recipients
• A donor cannot give to B recipients
• B donor cannot give to A recipients
• Any non-AB donor cannot give to AB recipients

Being incompatible doesn't prevent donation. It means exploring alternatives like paired exchange or desensitization protocols.

Crossmatching and antibody testing

Beyond blood type, the recipient may have antibodies against your tissue—acquired through prior transplants, pregnancies, or transfusions. The transplant center will test whether the recipient's blood serum will attack your cells using two approaches:

Crossmatching methods:

• Direct crossmatch tests your cells mixed with the recipient's serum to detect antibody binding
• Virtual crossmatch uses HLA typing to predict incompatibility without mixing blood

A positive crossmatch (antibodies present) typically prevents transplantation. However, desensitization protocols now exist that may allow transplantation despite a positive crossmatch in selected cases.

Paired exchange programs

If you and your intended recipient are blood type incompatible, paired kidney exchange offers a solution. You can trade—your kidney goes to someone else compatible with your blood type, and your intended recipient receives a kidney from a compatible donor. This exchange enables transplants that wouldn't otherwise be possible.

Paired exchange chains can involve multiple couples and sometimes include non-directed (altruistic) donors. The coordination is complex but highly sophisticated, using algorithms to identify compatible matches. When it works, the result is that incompatible pairs get transplanted when they might otherwise wait years on the deceased donor list.

Here's an example of how paired exchange works:

• You're O blood type; your sister is B (incompatible for direct transplant)
• Another O donor wants to give to a B recipient
• Your kidney goes to that B recipient; your sister receives a kidney from the B donor

Everyone gets a compatible kidney. You and your sister aren't transplanted with each other, but you both achieve your goals of donating and receiving. Some pairs join longer chains involving 3, 4, or even 5+ couples. The National Kidney Registry and other networks coordinate these complex exchanges nationally, significantly expanding transplant opportunities for incompatible pairs.

What if you are not a match?

If you're blood type incompatible and don't qualify for paired exchange, several alternatives exist:

Options for incompatible pairs:

• Blood type incompatible (BTI) transplantation using medications to reduce recipient's anti-blood type antibodies before surgery
• Non-directed donation to a compatible stranger while your intended recipient enters the paired exchange program
• Desensitization protocols if the issue is a positive crossmatch (HLA incompatibility)
• Waiting to see if circumstances change or if a deceased donor organ becomes available
• Pursuing alternative treatment options for your intended recipient

BTI transplants have good outcomes in experienced centers but require more intensive immunosuppression. Not all centers offer this, and not all recipients are good candidates. Desensitization for positive crossmatch is intensive and not universally available, but it's worth asking your center about.

HLA matching

Beyond ABO blood type, your HLA (human leukocyte antigen) typing affects how well your tissue matches the recipient's. Better HLA matching correlates with longer graft survival.

You're typed for HLA-A, HLA-B, and HLA-DR antigens. The recipient will have different HLA types. If your types are very different (0 antigen matches), graft survival is still good with modern immunosuppression—but it's slightly less ideal than a match (e.g., identical twins, who are 6/6 HLA matches).

For living donors, exact HLA matching is less critical than for deceased donors because the recipient can often start immunosuppression before surgery. Immunosuppressive medications are highly effective, and living donor kidneys last a long time even with HLA mismatch.