What is tissue typing for organ transplant?

Organ and tissue donation is often referred to as the gift of life, for good reason. A single donor has the potential to save up to eight lives through organ donation and heal more than 75 through tissue donation.

While the steps to sign up to be an organ donor are simple, the scientific process of matching donors and recipients for a transplant is a complex one.

It begins with tissue typing.

What is tissue typing?

Tissue typing ensures that an organ from a donor will be compatible with its recipient. The process starts with identifying the unique human leukocyte antigens (HLAs) for the organ donor and recipient, either from blood or tissue.

HLAs are an important part of the immune system’s response to foreign substances and act as a barcode to distinguish “self” from “non-self” — the latter resulting in rejection of the transplanted organ.

To date, more than 35,000 variations of the HLA protein have been identified. This makes it extremely difficult to find HLA-matched donors for transplant recipients. Half of a person's antigens are inherited from their mother and half from their father, so the more similar the antigen patterns are from two people, the more likely it is that those people are related. Identical twins have the same pattern, and brothers and sisters have a 1-in-4 chance of having an identical match.

During tissue typing, the recipient’s blood is also checked for the presence of preformed anti-HLA antibodies, created by the immune system when exposed to foreign tissue (usually from a previous transplantation, pregnancy or blood transfusion).

The final steps involve performing highly advanced assessments to evaluate the compatibility of the donor and recipient tissue, using tests that check for harmful interactions with the recipient’s blood that would damage the transplanted organ.

What kinds of tissue typing tests are performed?

Tissue typing can be done through routine testing and short-turn-around testing (STAT). When a deceased donor is identified, their unique HLA type and a technically complex test assessing the recipient’s compatibility is done STAT.

Routine testing is generally accomplished in batches. It takes about six hours to process 20 samples.

What happens if an organ donor and a recipient aren’t a match?

The closer the antigens match, the more likely it is that an organ or tissue transplant will succeed. A better match could reduce the amount of antirejection drugs required.

But even non-matches can lead to successful transplant: Sometimes, a person may agree to donate a kidney to a recipient, but their blood or tissue type does not match their recipient. In those cases, kidney paired donation (kidney exchange) can help match such a donor/recipient pair with another donor/recipient pair. This allows the two recipients to receive organs from two people who were willing to donate, even though the original pairings were incompatible.

Paired donation can also involve multiple donors and recipients. In recent years, The Ohio State University Wexner Medical Center’s Comprehensive Transplant Center has performed a number of large living donor chains. An eight-way chain is currently the largest single-institution living donor kidney transplant chain performed in Ohio to date.