Organ Donation Glossary
Key terms and definitions to help you understand organ donation, transplantation, and related policy.
Allocation
The system used to distribute donated organs to patients on the waiting list. In the US, UNOS manages allocation based on medical urgency, blood type, time on the waitlist, geographic proximity, and other factors.
Altruistic Donation
An organ donation from a living donor to a stranger, without any prior relationship. Also called non-directed donation. Altruistic donors are often the starting point for kidney paired exchange chains.
Brain Death
The irreversible loss of all brain function, including the brainstem. Brain death is the legal standard for death in organ donation cases. It must be declared by physicians who are not part of the transplant team.
Bioethics
The study of ethical issues arising from advances in biology and medicine. In organ donation, bioethics covers topics like consent, allocation fairness, living donation risks, and the definition of death.
Cadaveric Donation
Organ donation from a deceased person. Also called deceased donation. Most organ transplants come from cadaveric donors, either after brain death or circulatory death.
Cold Ischemia Time
The time an organ is preserved outside the body (on ice or in preservation solution) between removal from the donor and transplantation into the recipient. Shorter cold ischemia times generally lead to better outcomes.
Crossmatch
A blood test performed before transplantation to check whether the recipient's immune system will react against the donor's organ. A negative crossmatch (no reaction) is required for most transplants to proceed.
Deceased Donor
A person who has died and whose organs or tissues are recovered for transplantation. Deceased donors may donate after brain death (DBD) or after circulatory death (DCD).
Dialysis
A medical treatment that performs the functions of the kidneys when they fail. Hemodialysis filters blood through a machine; peritoneal dialysis uses the lining of the abdomen. Many kidney transplant recipients were on dialysis before their transplant.
HLA (Human Leukocyte Antigen)
Proteins on the surface of cells that help the immune system distinguish between the body's own cells and foreign ones. HLA matching between donor and recipient affects transplant success rates.
Histocompatibility
The degree of immunological similarity between the tissues of a donor and a recipient. Higher histocompatibility means a lower risk of organ rejection after transplantation.
Immunosuppression
The use of medications to suppress the immune system's response to a transplanted organ. Transplant recipients take immunosuppressant drugs for life to prevent organ rejection.
Informed Consent
The process by which a person makes a voluntary, knowledgeable decision about medical treatment — including organ donation. In opt-in systems, informed consent means actively choosing to register.
Kidney Paired Donation
A system where incompatible donor-recipient pairs are matched with other pairs in a chain. Donor A gives to Recipient B, Donor B gives to Recipient C, and so on — so everyone gets a compatible kidney.
Living Donor
A person who donates an organ (usually a kidney or part of the liver) while alive. Living donors undergo thorough medical and psychological evaluation to ensure donation is safe for them.
LVAD (Left Ventricular Assist Device)
A mechanical pump implanted in the chest to help a weakened heart pump blood. LVADs can be used as a bridge to transplant while waiting for a donor heart or as long-term therapy.
Opt-In System
An organ donation system where individuals must actively register to become donors. This is the current system in New York State and most of the United States. People who don't register are not considered donors.
Opt-Out System
An organ donation system where individuals are automatically registered as donors unless they explicitly choose not to be. Also called presumed consent. Used in over 30 countries, including Spain, France, and the UK.
OPO (Organ Procurement Organization)
A federally designated organization responsible for coordinating organ recovery from deceased donors in a specific geographic area. There are 56 OPOs in the United States.
OPTN (Organ Procurement and Transplantation Network)
A public-private partnership that connects all professionals involved in the US organ donation and transplantation system. UNOS currently holds the federal contract to operate the OPTN.
Presumed Consent
The principle behind opt-out organ donation systems: it is assumed that all citizens consent to organ donation after death unless they have explicitly registered their objection during their lifetime.
Rejection
An immune response where the recipient's body attacks the transplanted organ, recognizing it as foreign. Rejection can be acute (sudden) or chronic (gradual). Immunosuppressant medications help prevent it.
Donor Registration
The process of signing up to be an organ and tissue donor. In New York, you can register at the DMV, online through the NY Donate Life Registry, or by texting REGISTER to 57838.
Transplant
A surgical procedure in which a failing organ or tissue is replaced with a healthy one from a donor. Common transplants include kidney, liver, heart, lung, pancreas, and cornea.
Tissue Typing
Laboratory tests that determine the HLA antigens on a person's cells. Tissue typing is used to find the best match between organ donors and recipients to minimize the risk of rejection.
UNOS (United Network for Organ Sharing)
The private nonprofit organization that manages the US organ transplant system under federal contract. UNOS maintains the national transplant waiting list and develops policies for organ allocation.
UAGA (Uniform Anatomical Gift Act)
A uniform state law that provides the legal framework for organ and tissue donation in the United States. The UAGA allows individuals to make legally binding decisions about donation before death.
Transplant Waitlist
The national list of patients waiting for organ transplants, managed by UNOS. Over 103,000 Americans are currently on the waitlist. Wait times vary by organ type, blood type, and geographic location.
Xenotransplantation
The transplantation of organs, tissues, or cells from one species to another — typically from genetically modified pigs to humans. Xenotransplantation is an active area of research that may help address the organ shortage in the future.
Zero Mismatch
A situation where the donor and recipient share all six major HLA antigens. Zero-mismatch transplants have the best long-term outcomes and the lowest risk of rejection.
Want to Learn More?
Explore our FAQ for common questions or visit our Facts page for key statistics about organ donation.