BERLIN—Long-term failure rates of transplanted kidneys are more than 30% higher in the U.S. than in Australia, New Zealand, and the U.K., a new study shows.

“We have some hypotheses regarding the findings, and believe that they may related to fundamental differences in the health-care delivery system in the U.S. compared to the other three countries represented in the study,” said lead investigator Robert Merion, MD, President of Arbor Research Collaborative for Health and Professor of Surgery at the University of Michigan, both in Ann Arbor. “Although we did account for a wide variety of factors that are known to affect graft outcome in our analyses, it is possible that there are unmeasured differences in patient comorbidities.”

Dr. Merion, who presented the results at the 24th International Congress of The Transplantation Society, said he was surprised at the magnitude of the difference.

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He and his co-investigators previously had performed preliminary registry-specific analyses of unadjusted graft outcomes. To extend these findings, they conducted risk-adjusted analyses of data from the Scientific Registry of Transplant Recipients in the U.S., the organ-donor registry of the U.K.’s National Health Service Blood and Transplant organization and the Australia and New Zealand Dialysis and Transplant Registry.

They examined data from 259,531 kidney transplants in the United States, 34,776 in the United Kingdom, 10,655 in Australia, and 2,036 in New Zealand, all of which took place between 1988 and 2010. Median patient follow-up was 6.7 years.

The researchers found significantly higher proportions of living-donor transplants in the U.S., Australia, and New Zealand (37%, 34%, and 36%, respectively) compared with the U.K. (20%). Furthermore, 23% of recipients in the U.S. received transplants for diabetic nephropathy compared with only 9% in the U.K. and 6% in Australia and New Zealand. The study also revealed a higher proportion of zero human leukocyte antigen (HLA)-mismatched transplants in the U.S. (10% vs. 9% in the U.K. and 6% in Australia and New Zealand).

The proportion of adjusted graft failure was 30% higher at one year in the U.K. and New Zealand than in the U.S. Long-term graft failure, however, was 30% higher in the U.S. than in the each of the other three countries studied. The overall risk of graft failure was lower in more recent years, the researchers noted. However, the magnitude of this improvement was significantly greater in the U.K., Australia, and New Zealand than in the U.S.

The effects of recipient sex, donor age (40 years and older) and type, and cause of death on the risk of graft loss were not significantly different between the three registries. However, the effects of recipient age, race, diagnosis, donor age (among donors under 40) and sex, number of HLA mismatches, and year of transplant were significantly different in the U.S. compared with the other three countries.