Particulate Constituents and Posttransplant Outcomes Among Kidney Transplant Recipients

Total particulate matter with a diameter of 2.5 µm or less (PM2.5) has been found to be associated with adverse posttransplant outcomes among kidney transplant (KT) recipients. However, PM2.5 is a complex mixture of multiple constituents, all of which have different toxicity profiles, so it is not clear which constituents are most associated with adverse outcomes among KT recipients.

To investigate the associations between PM2.5 constituents and post-KT outcomes among KT recipients.

This cohort study was conducted among patients who received a KT between January 2000 and December 2016 and lived in the contiguous United States. Follow-up continued through December 2021, and data were analyzed from August 2023 to May 2025.

Fifteen PM2.5 constituents (including elemental carbon, ammonium, nitrate, organic carbon [OC], sulfate [SO42-], bromine, calcium, copper, iron, potassium, nickel [Ni], lead [Pb], silicon, vanadium, and zinc) at the zip code of residence prior to KT, estimated from ensembled machine learning models.

Adverse post-KT outcomes included acute rejection, delayed graft function (DGF), death-censored graft failure (DCGF), and mortality. The association of PM2.5 constituents and the outcome were evaluated with weighted quantile sum regressions.

In total, 192 587 KT recipients were included in the analysis (mean [SD] age at transplant, 51.56 [13.47] years; 75 021 [39.0%] female; 51 455 [26.7%] Black, 28 586 [14.8%] Hispanic, and 97 927 [50.8%] White). Each decile increase in the PM2.5 constituent mixture was associated with a 6.8% (95% CI, 5.8%-7.8%) and 3.6% (95% CI, 2.1%-5.1%) increase in the odds of DGF and acute rejection, respectively. OC and Ni contributed the largest weights to the observed association between PM2.5 mixture and DGF (OC: relative importance, 35.6%; Ni: relative importance, 34.4%), while Pb had the largest impact on acute rejection (relative importance, 75.0%). Each decile increase in PM2.5 constituent mixture was associated with a 4.7% (95% CI, 3.3%-6.3%) and 3.9% (95% CI, 2.5%-5.2%) increase in the hazard of DCGF and all-cause mortality, respectively. The constituent that contributed the largest weight to the observed association between PM2.5 mixture and long-term post-KT outcomes was SO42- (relative importance, 51.3%).

In this cohort study, PM2.5 constituents were associated with an increased risk of adverse posttransplant outcomes among KT recipients. Of the PM2.5 constituents included in this study, SO42- contributed most to long-term outcomes, while Pb, OC, and Ni were more associated with short-term outcomes.