Double dose: two ways to boost kidney-transplant viability.

By testing the blood-purifying capacity of kidneys obtained for transplant from people 60 years or older--then culling the worn-out kidneys--scientists have identified organs likely to last in their new hosts. To bolster a recipient's odds, researchers transplanted the older kidneys in pairs.

The measures could expand the number of kidneys available to patients, says study coauthor Giuseppe Remuzzi, a nephrologist at Mario Negri Institute for Pharmacological Research in Bergamo, Italy.

There's a shortage of good kidneys for transplant. In the United States, about 65,000 people with severe kidney disease are candidates for a transplant. Yet only about 16,000 of them will find a matching donor this year. Nearly all will get a single kidney. More than half of the transplants come from brain-dead donors or cadavers; the others come from a living relative or an unrelated donor.

Within 10 years, nearly two-thirds of kidneys transplanted from brain-dead donors or cadavers fail, defined as a decline in blood-filtering capacity to a point at which the person needs dialysis. Many of these people go back on the waiting list for a new kidney.

In the new study, doctors gave transplant candidates two options for receiving kidneys from brain dead-donors: get on a waiting list for a single kidney from a person of unknown age or receive one or two kidneys from a person age 60 or older.

For the latter group, doctors went beyond standard practice by taking biopsies of potential transplant kidneys before they were removed. The team evaluated an organ's supply of healthy nephrons--the kidneys' blood-filtering cell clusters. Kidneys lose nephrons over the years, and in this experiment, only organs with a good supply of nephrons were removed and transplanted.

Of the 62 patients electing to get the screened kidneys from an older person, almost all received a pair. The standard-transplant group was made up of 248 patients. Each patient received one unscreened kidney; half came from a donor under age 60 and half from someone 60 or over. The physicians matched donors and recipients for immune compatibility.

During 2 years of follow-up, the researchers found that of patients receiving a pair of older kidneys that were tissue tested before transplant, about 6 percent had kidney failure. That same percentage failed among untested kidneys obtained from donors under age 60. However, 23 percent of untested kidneys from donors age 60 and over failed, the researchers report in the Jan. 26 New England Journal of Medicine.

The study supports the view of nephrologist Barry M. Brenner of Harvard Medical School and Brigham and Women's Hospital in Boston, who maintains that the future well-being of a transplanted kidney is in large part governed by its number of functional nephrons. Since the 1990s, Brenner has argued that nephrons are the overlooked players in kidney transplants. He notes that small kidneys transplanted into large people have a high failure rate, probably because the nephrons become overworked.

When tests show that their nephron numbers are marginal, Brenner advocates transplanting kidneys from brain-dead donors in pairs, and hence delivering more nephrons. While transplanting two kidneys into a single recipient might limit the number of organs available to other people in the short term, the kidneys would last longer and reduce the number of transplant recipients returning to the waiting list, he says.