UNOS gives preference to people who have been on the waiting list the longest. However, other factors-such as your age, where you live, and your blood type-may make your wait longer or shorter. Wait times can range from a few months to several years.

If you have a living donor, you do not need to be placed on the waiting list and can schedule the surgery when it is convenient for you and your donor.

While you are on the waiting list, notify the transplant center of changes in your health. Also, let the transplant center know if you move or change phone numbers. The center will need to find you immediately when a kidney becomes available.

While you wait for a kidney, you will have blood drawn once a month. The sample will be sent to the transplant center. The center must have a recent sample of your blood for comparison with any kidney that becomes available.

Organ procurement organizations identify potential organs for transplant and coordinate with the national network. When a deceased donor kidney becomes available, the organ procurement organization notifies UNOS and creates a computer-generated list of suitable recipients.

Whether you are receiving your kidney from a deceased donor or a living donor, the transplant team considers three factors in matching kidneys with potential recipients. These matching factors help predict whether your body’s immune system-which protects your body from infection by identifying and destroying bacteria, viruses, and other potentially harmful foreign substances-will accept or reject the new kidney.

• Blood type. Your blood type-A, B, AB, or O-must be compatible with the donor’s. Blood type is the most important matching factor. Some transplant centers have developed techniques for transplanting kidneys that are not matched by blood type.
• Human leukocyte antigens. These six antigens are proteins that help your immune system tell the difference between your own body’s tissues and foreign substances. You may still receive a kidney if the antigens do not completely match, as long as your blood type is compatible with the organ donor’s blood type and other tests show no problems with matching.
• Cross-matching antigens. The cross-match is the last test performed before a kidney transplant can take place. A lab technician mixes a small sample of your blood with a sample of the organ donor’s blood in a tube to see if the mixture causes a reaction. If no reaction occurs-called a negative cross-match-the transplant can proceed.