A nationwide system of exchanging kidneys for transplantation to achieve the best tissue match could significantly improve the success rate of the operations, researchers said this week.

The results of a 3-year-old program in which 170 transplantation centers exchanged about 600 kidneys taken from cadavers showed an estimated 5 percent improvement in long-term survival of organs, said Paul Terasaki of the UCLA Tissue Typing Laboratory in Los Angeles.The increase in organ survival as a result of better tissue matching is nearly equivalent to that brought about by the introduction of the anti-rejection drug cyclosporine in the early 1980s, Terasaki and colleagues reported in The New England Journal of Medicine.

A study of the kidney exchange program left "no doubt" that matching the tissue of the transplanted organs as closely as possible with those of patients significantly improved one-year and 10-year success rates, Terasaki said.

About 8,000 kidney transplants are conducted annually in the United States, with about 80 percent of organs coming from cadavers and 20 percent from living donors - usually relatives of recipients.

Kidney problems can be caused by various disorders, including diabetes and high blood pressure. Because kidneys work as filters to remove waste from the body, untreated kidney disease can result in death.

Currently, about 80 percent of kidneys from cadavers are properly functioning after one year, compared to about 90 percent to 95 percent of those from living donors.

However, Terasaki said even with the use of cyclosporine - which decreases the immune system's ability to reject a transplanted kidney - the 10-year survival rate for cadaver kidneys is only 32 percent.

When transplanted kidneys fail, the patient either has to undergo kidney dialysis or undergo another transplant operation. "Some patients might need as many as five transplants before they reach age 60," Terasaki said.

The new study indicates the average 10-year organ survival rate could be increased to 37 percent if transplant centers and doctors agreed to exchange kidneys nationwide to get the best tissue matches, he said.

At the present time, most hospitals prefer to keep the cadaver kidneys they have for local use, even if the match-up between tissue and recipient is not that close, he said.

In addition, many doctors think sending an organ across the country to another hospital could lead to delays that might damage the organ and make it more likely to be rejected, he said.