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 1st of 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 6 209 records, a total of 6 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% 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.