Inadequate Donor Size in Cadaver Kidney Transplantation BERTRAM L. KASISKE,* † JON J. SNYDER,* and DAVID GILBERTSON* *The United States Renal Data System Coordinating Center, Minneapolis, Minnesota; and † Department of Medicine, Hennepin County Medical Center, Minneapolis, Minnesota. Abstract. There have been conflicting reports that kidneys from small donors may be at increased risk for late graft failure if they are transplanted into large recipients. Data from the United States Renal Data System was used to study all first cadaver kidney transplantations performed during the years 1994 to 1999. Donor and recipient body surface area (BSA) combinations were included along with other patient and trans- plant characteristics in a Poisson analysis of factors associated with early (in the first 4 mo) and late (4 mo) graft failure. The numbers of large (BSA 2.2 m 2 ) and medium size (BSA 1.6 to 2.2 m 2 ) recipients that received kidneys from small (BSA 1.6 m 2 ) donors are less than expected ( 2 = 118.09; P  0.0001), suggesting that transplant centers may be refusing some kidneys on the basis of donor-recipient size differences. Large recipients who received kidneys from small donors made up 1.5% of the population and had a 43% (95% CI, 17 to 75%; P = 0.0004) increased risk of late graft failure compared with medium-size recipients who received kidneys from medium- size donors (53.4% of the population). Medium-size recipients who received kidneys from small donors made up 12.0% of the population and had a 16% (95% CI, 6 to 26%; P = 0.0012) increased risk of late graft failure. Disparities in recipient and donor size had similar adverse affects on mortality. Effects of recipient obesity (body mass index) and donor gender on late graft survival were no longer statistically significant after the effects of donor and recipient body size were taken into ac- count. In conclusion, the relative size of the donor and recipient should possibly be taken into account when choosing kidneys for transplantation. The theory that compensatory increases in glomerular capillary pressures and flows contribute to chronic progressive kidney damage has played a prominent role in nephrology. We know that reducing kidney mass causes progressive injury in the remaining remnant kidney in animal models (1,2). We also know that compensatory increases in glomerular capillary pres- sure, flow, and filtration, e.g., “hyperfiltration”, are associated with progressive injury in the rat remnant kidney (3). However, direct evidence to support this hypothesis in humans still does not exist. In the past decade, several investigators suggested that hy- perfiltration injury from “inadequate nephron dosing” may cause progressive injury in transplanted human kidneys. Ac- cording to this theory, a large patient who receives a small kidney may develop some of the same compensatory changes originally described in the rat 5/6 nephrectomy model (4,5). Although it is not possible to directly measure glomerular hemodynamics in humans, the hypothesis can be indirectly tested if we assume that large individuals have a greater renal functional capacity than smaller individuals. Body size, mea- sured as body surface area (BSA), correlates with glomerular volume (6,7), kidney weight (6,7), and GFR (8,9). Therefore, a reasonable test of the hypothesis is to examine the effects on long-term graft survival of placing a kidney from a small (low BSA) donor into a large (high BSA) recipient. Studies in individual transplant centers have produced con- flicting results. Some investigators have reported reduced graft survival in situations in which the size of the donor kidney would be expected to be reduced in proportion to the size of the recipient (10,11). Other single-center studies found no effect of donor-recipient size mismatching on graft survival (12–17). However, many of these studies may have lacked adequate statistical power to test the hypothesis rigorously. Studies using data collected by the United Network for Organ Sharing (UNOS) have shown that graft survival is generally reduced in recipients with greater body weight, body mass index (BMI), and/or BSA (18,19). Unfortunately, UNOS did not begin col- lecting data on donor size until 1994, so the effects of donor- recipient size mismatching on long-term outcomes has never been examined. At the 16 th International Congress of the Transplantation Society in 1996, Cho et al. (20) reported that size mismatching was associated with decreased 1-yr graft survival. However, the duration of follow-up was short, and this analysis did not adjust for potential confounding effects from donor and recipient age or gender or other factors (20). We used data from UNOS and the United States Renal Data System (USRDS) to examine the effects of donor-recipient size mismatching on long-term patient and graft survival after kid- ney transplantation. We particularly investigated whether the effect of size mismatching was simply due to an effect of obesity in the recipient per se or whether it could have been due to effects of size mismatching that were independent of obesity. In addition, we hypothesized that the effects of hyper- Received April 12, 2002. Accepted May 20, 2002. Correspondence to Dr. Bertram L. Kasiske, Department of Medicine, Henne- pin County Medical Center, 701 Park Avenue, Minneapolis, MN 55414. Phone: 612-347-6088; Fax: 612-347-2003; E-mail: kasis001@umn.edu 1046-6673/1308-2152 Journal of the American Society of Nephrology Copyright © 2002 by the American Society of Nephrology DOI: 10.1097/01.ASN.0000024564.22119.3D J Am Soc Nephrol 13: 2152–2159, 2002