Association between air pollution and transplant outcomes in kidney transplant recipients: a systematic review and meta-analysis.

Background: Emerging evidence suggests that ambient air pollution may adversely affect long-term outcomes in kidney transplant recipients; however, quantitative estimates across clinical endpoints remain limited. This meta-analysis aimed to systematically evaluate the association between air pollution exposure and mortality, graft failure, and rejection risk in kidney transplant populations.

Methods: A systematic database search was carried out across the databases of the Cochrane Library, Web of Science, Scopus, and PubMed until the 1 May 2025. Research that evaluated the impact of air pollution, particularly PM₂.₅, PM₁₀, NO₂, O₃, and other ambient pollutants, on graft survival in kidney transplant recipients were evaluated. Hazard ratios (HR) were extracted or recalculated for all-cause mortality, death-censored graft failure, and graft rejection per 10 µg/m³ increase in particulate matter concentration.

Results: After screening 6209 records, a total of six studies involving populations of adult kidney transplant recipients from the USA, UK, South Korea, and Taiwan were included in the meta-analysis. Exposure to ambient air pollution was significantly associated with increased all-cause mortality among kidney transplant recipients [pooled HR 1.61; 95% confidence intervals (CI) 1.01-2.58], as well as higher risks of death-censored graft failure (HR 1.25; 95% CI 1.04-1.50) and graft rejection (HR 1.35; 95% CI 1.09-1.69) per 10 µg/m³ increment in particulate matter concentration. Substantial heterogeneity was observed across studies, particularly for mortality (I² = 99%) and graft rejection (I² = 91%). No significant associations were found between air pollution exposure and cardiovascular disease or coronary heart disease mortality.

Conclusion: Ambient air pollution exposure is associated with increased risks of mortality, graft failure, and rejection in kidney transplant recipients, highlighting air pollution as a modifiable environmental risk factor that may have important implications for long-term transplant outcomes.