Mortality in the general population and in patients on chronic hemodialysis is significantly higher in winter than summer. It is unknown whether such a seasonal difference exists for mortality or graft failure among kidney transplant recipients. We analyzed United Network for Organ Sharing (UNOS) data to assess whether the annual distribution of deaths and graft failures differed significantly from expected. There was significant annual variation in both deaths (n = 52 523) and graft failures (n = 50 301; both P < 0.001). The number of observed deaths exceeded the number expected by 8.9% in winter (P < 0.001), whereas the number of deaths was 4.8% lower than expected in summer (P < 0.01). The pattern was strongest for deaths attributable to cardiovascular disease (n = 11 509; 21.9%). Similarly, there was an excess of graft failures in winter (3.6%; P < 0.01) and a deficit in other seasons (all P ≤ 0.02). This pattern was observed for graft failures due to chronic rejection (P < 0.001) and other causes (P < 0.001), but not for acute rejection (P = 0.28) or recurrent disease (P = 0.27). Potential explanations for this variation include changes in physiologic parameters, changes in medication adherence and other behaviors, or changes in insurance coverage or clinical care. Further studies are necessary to identify specific mechanisms.
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