Identification of a previously unrecognized signal of kidney transplant rejection will help doctors detect and treat the problem earlier, researchers reported at the American Society of Nephrology’s Kidney Week meeting in San Diego.

Their study showed microvascular inflammation, or inflammation in even the tiniest blood vessels around the kidneys, “predicts trouble down the road," study leader Vikas Dharnidharka, MD, of Rutgers Robert Wood Johnson Medical School in New Jersey said in a statement.

In 2022, surgeons around the world began to collect biopsy data on microvascular inflammation to determine whether it was in fact a warning sign. For the current study, they analyzed biopsies obtained from 6,798 kidney recipients in Europe and North America between 2004 and 2023.

Among the more than 16,000 biopsies, 503 showed microvascular inflammation but no other typical signs of rejection. Yet these patients had more than twice the five-year graft-failure risk as patients with no signs of organ rejection, according to a report in The New England Journal of Medicine.

Another 285 biopsies showed some mild inflammation, with a minimal amount of antibodies present, that in the past would not have been interpreted as showing rejection. Patients with these biopsies were nearly three times as likely to experience graft failure than patients with no such signs.

Patients with these findings were also at higher risk for more severe rejection or chronic kidney damage over time.

"These data indicate that we should be treating patients who fall into these categories differently," and doing tests to determine what those treatments should be, Dharnidharka said.