DEAR MAYO CLINIC: Why, if you're at the top of the transplant list, would you not be able to get a donor organ when one becomes available?

ANSWER: Patients at the top of the list are given consideration when a potential organ becomes available. But time on the list is only one factor when the transplant team decides who will receive the transplanted organ.

Many factors may preclude a given individual from receiving the available organ, such as:

The immunology isn't right: Even when blood types are matched or compatible, a recipient's antibodies can react to the antibodies present in the donated organ, causing rejection of the transplanted organ.

With living donors for kidney transplants, this antibody screening is done early to know if a potential donor is a good match. With deceased donors, the lab test may be in the works as the recipient is called in for possible transplant surgery. If the antibodies indicate a mismatch, the transplant team considers other possible recipients. This situation can occur with kidney, pancreas, heart and lung transplants.

The organ is the wrong size: A liver, heart or lungs from a 12-year-old child or 5-foot-2-inch adult may not be adequate for a potential recipient who is 6 feet 3 inches tall. These organs will perform better in smaller recipients. For kidneys and pancreas, size usually isn't a concern.

The organ isn't healthy enough: This situation comes up with liver transplants. When a medical team harvests organs, they may find that the liver is fatty, inflamed, or cirrhosis is present. While other organs from this donor may be available, an unhealthy liver would not be transplanted.

Where you live: In reality, there is no single waiting list. Organs are made available through 11 regions in the United States, and the differences in typical waiting times are huge. Some regions, because of higher population density and/or fewer donors, have longer wait times. The national mean waiting time for a kidney transplant is 1,763 days, according to the Organ Procurement and Transplantation Network. The mean waiting time in region 4 (Texas and Oklahoma) is as low as 1,203 days, and in region 5 (Arizona, California, Nevada, New Mexico and Utah), it's as high as 2,047 days. In region 9 (New York and Vermont), the mean waiting time is 2,520 days.

The regional differences in wait time occur for other organs, too. Wait times for transplant depend not only on how sick you are, but where you live. Work is under way to improve this situation. A small percentage of patients have the flexibility and resources to travel where organ availability is best. But, right now, some patients are penalized by geography.

If there's a possibility that a donated organ will work for a given individual, we'll do everything we can to make the transplant happen. But sometimes the situation is a no-go. That decision may be made after a potential recipient has been called to the hospital. Some patients may be alerted to a potential donated organ two or three times before the transplant occurs. While we strive to minimize these no-go situations, they occur perhaps 15 to 20 percent of the time.

In 2009, more than 106,000 people in the United States were waiting for organs to save their lives, and about 28,500 transplants were performed. The best way to assure that patients receive lifesaving transplants is to increase the number of donors. To learn more about organ donation, visit http://OrganDonor.gov.

-- David Mulligan, M.D., Hepatology/Transplant Surgery, Mayo Clinic in Arizona

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