BERLIN—Donor/recipient body surface area (BSA) ratio should be taken into account when matching living donors with children who need a kidney transplant, investigators from Seattle Children’s Hospital concluded.

The team used data from the United Network of Organ Sharing’s Standard Transplant Analysis Research (UNOS STAR) files to show that a donor/recipient BSA ratio below 0.9 is associated with a 59% increased risk of graft loss by 10 years after kidney transplant in the pediatric population (younger than 18 years).

“When kids get a kidney transplant, at some point in their lives they’re going to need another, so the goal is to maximize the longevity of that graft,” said lead investigator André Dick, MD, MPH, after presenting the results at the 24th International Congress of The Transplantation Society. Dr. Dick is Assistant Professor of Surgery in the Division of Transplantation at the University of Washington and Seattle Children’s Hospital.

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Using the UNOS STAR database, he and his colleagues identified 3,089 living donor-pediatric recipient pairs with a donor/recipient BSA ratio of 0.9 or greater and another 112 pairs with a ratio below 0.9. The donor demographics were similar in the two groups, with the average age being 37-40 years and 66%-71% being white. In the lower donor/recipient BSA ratio group 83.9% of donors were female compared with 54.7% in the other group.

The recipients in the lower-BSA ratio group were significantly older (16.7 vs. 11.0 years), and the respective proportion of males was 78.6% and. 59.3%. Lower-BSA-ratio recipients also were more likely to have glomerulonephritis as the cause of their renal failure and less likely to have a cystic, congenital, or hereditary cause. This is consistent with the causes of renal disease in the adolescent population. The clinical characteristics of the two groups, including cold or warm ischemia times, were similar.

In the lower donor/recipient BSA ratio group, donated kidneys often came from relatively small females and were transplanted into larger, older male recipients.

Fifty percent of the grafts were lost after 6.8 years in the donor/recipient body surface area ratio group below 0.9 while this occurred after 10.8 years in the group with a donor/recipient body surface area ratio of 0.9 or higher.

Few studies have been done on the effects of donor/recipient BSA ratio in children because pediatric kidney transplants are far less common than those in adults. One of the seminal studies was by an Italian group (Pediatr Transplant 2009;13:290-296). They showed that a ratio of 0.8, in the deceased donor population, or less was associated with a 35.7% rate of acute rejection; a ratio of 0.81-1.19 had a 38.9% rate and a ratio of 1.2 or greater was associated with an 18.8% rate.

“One hypothesis is that with small ratios the small kidney has to compensate for the metabolic demands of the larger recipient, leading to progressive injury, which in turn affects long-term graft survival,” Dr. Dick said.