Higher Heat Index Tied to Adverse Kidney Transplant Outcomes

Patients undergoing kidney transplantation in regions with the highest heat indexes show increased rates of kidney function decline and major adverse kidney events (MAKEs) compared with recipients of transplants performed in cooler environments, according to a study of 250 kidney transplant centers in the United States.

“In US kidney transplant recipients, higher heat exposure was independently associated with a modest progressive kidney transplant function decline and increased MAKE risk compared to lower heat exposure,” reported first author Gabriel Cojuc-Konigsberg, MD, Beth Israel Deaconess Medical Center, Boston, at the National Kidney Foundation (NKF) 2025 Spring Clinical Meetings.

“Preventing heat exposure in kidney transplant recipients should receive higher priority in research, public health efforts, and clinical practice to prevent adverse kidney transplant outcomes,” he said.

Ambient heat exposure has been associated with worsening kidney outcomes in a variety of contexts, including potentially aggravating existing chronic kidney disease (CKD), causing acute kidney injury, and increasing the risk for kidney stone episodes, Cojuc-Konigsberg noted.

Additional research has shown that agricultural workers in tropical and subtropical regions are disproportionately affected by CKD, and these concerns have intensified under the threat of climate change.

“While the exact mechanisms of this association remain unknown, rising global temperatures pose significant threats to kidney health,” Cojuc-Konigsberg said.

To further investigate the role of heat exposure among kidney transplant recipients, Cojuc-Konigsberg and colleagues retrospectively reviewed 63,351 kidney transplant recipients identified in the UNOS-STAR cohort, who were transplanted between 2010 and 2023 and had at least two serum creatinine measurements within a year of transplant.

The patients had a mean age of about 53 years and approximately 39% were women. Most patients, about 53%, were treated with tacrolimus.

The 250 kidney transplant centers in the study were categorized as hot, with at least 12 months in which there was heat index of at least 30 °C in their location during the study period, or cold, with fewer than 12 months with a heat index of at least 30 °C. The heat index in the study was calculated based on perceived heat, including factors such as humidity and ambient dry temperature.

Overall, 58 of the centers (23%), where 14,901 (23%) of transplant recipients were treated, were classified as hot.

With a median follow-up of 4.9 years and four serum creatinine measurements, and after a multivariate adjustment, each additional year with an average heat index of at least 30 °C was associated with an average annual decrease in estimated glomerular filtration rate (eGFR) of −0.62%.

In addition, kidney transplant recipients who were transplanted in hot settings had a 30% increase in the risk for MAKE, a composite of death from any cause, graft failure, or doubling of serum creatinine, compared with kidney transplant recipients in cold centers (adjusted hazard ratio [aHR], 1.30; P < .001).

“In our primary analysis, we observed that increased heat exposure was associated with the progressive and faster eGFR decline,” Cojuc-Konigsberg said.

No differences were observed based on donor type (living or deceased), or the use of tacrolimus at discharge, however, of note, individuals with a lower baseline eGFR had a more rapid eGFR decline associated with heat exposure.

“Overall, we found that among individuals exposed to heat exposure, each additional year with a heat index above 30 °C was associated with a 30% higher risk of major adverse kidney events, defined as death, graph failure, or doubling of serum creatinine,” Cojuc-Konigsberg said.

Volume Depletion, Immunological Status Risk Factors?

Commenting on the study, Samira Farouk, MD, associate professor of medicine and medical education at Icahn School of Medicine at Mount Sinai, New York City, noted that a variety of factors could play a role in the effects of heat exposure on the kidneys.

“First, we know that volume depletion, in which people are dehydrated, is associated with acute kidney injury; and uric acid levels related to heat exposure may be damaging to the kidneys over time,” she told Medscape Medical News.

“Secondary factors could include access to clean water in some hot environments,” she added. Furthermore, hotter climates may predispose patients to certain infections, such as mosquito-borne diseases.

Another consideration, particularly with kidney transplant recipients, is the role of heat exposure in people at immunological risk.

“We know that other environmental exposures, such as the diet, pollutants in the air, and microbes that someone is exposed to can impact how the T cells are activated and behaving, so I think heat exposure could play into this as well,” Farouk said.

“We don’t really have a good way of knowing how immunosuppressed someone is, and so it would be interesting to understand if being in a hotter climate has an impact on the immune system,” she said.

Farouk noted that encouraging kidney transplant recipients to stay hydrated is already a significant challenge, but the new findings underscore the importance of doing so.

“It is very important for kidney transplant recipients to drink water and try to maintain their volume status, which can be a challenge for someone having a transplant because if they have been on dialysis for many years, they may have been told to not drink much, and then they have a transplant organ making a lot of urine and are then told to drink more water,” she said.

“So if you add to that to a hot climate, I can imagine that [staying hydrated] becomes even more important, particularly now with this data.”

Cojuc-Konigsberg and Farouk had no disclosures to report.