Study: urine test could make more donor kidneys available

A urine test that can produce results within 30 minutes could change the moment when a deceased donor kidney is judged usable or too risky. Researchers at Johns Hopkins Medicine found that three urinary biomarkers—uromodulin, osteopontin and YKL-40—made predictions of long-term transplant function more accurate when added to the Kidney Donor Profile Index, or KDPI, the score commonly used to estimate a donor kidney's risk from age and medical history.

The difference was measurable: prediction accuracy increased from 80% with the KDPI alone to 86% with the biomarkers included. The method also improved identification of kidneys likely to produce favorable outcomes by 10 percentage points, while maintaining a specificity of 78%. The study analyzed 474 deceased donors whose kidneys were transplanted into paired recipients, allowing the researchers to compare how donor-kidney quality shaped outcomes over three years.

The mechanism is straightforward. The KDPI mainly describes the donor; the urine biomarkers offer a direct signal from the kidney itself. Senior author Chirag R. Parikh, director of the Division of Nephrology at Johns Hopkins University School of Medicine, said the markers can indicate whether the kidney is repairing—information that a single creatinine measurement and a medical history cannot provide. The panel performed similarly with laboratory immunoassays and rapid lateral-flow devices.

The practical payoff could be largest for kidneys that currently sit in the gray zone. Using data from more than 1,500 deceased donors, the researchers modeled a process that could reduce unnecessary biopsies in approximately 20% of donors and return at least one kidney to the transplant pool for about 7% of donors whose organs would otherwise not be used. In a hypothetical group of 10,000 donors, that amounts to more than 2,000 avoided biopsies and approximately 700 additional kidneys available for transplantation.

And then what? For people waiting for a kidney, a faster read on organ health could mean fewer potentially usable organs are discarded and more decisions are made with biological evidence rather than uncertainty. More than 92,000 people are currently waiting for a kidney transplant in the United States, while nearly one in four recovered donor kidneys goes unused each year, according to the American Kidney Fund. The researchers stress that these findings are observational: the test is not yet standard practice, and its next step is prospective, real-time use during donation.