BACKGROUND: Studies estimating risks after cardiac surgery for patients receiving kidney replacement therapy have been limited by the size and generalizability of those cohorts. This study used data linked between registries to estimate short-term postoperative outcomes for large patient cohorts receiving kidney replacement therapy at the time of surgery. METHODS: This population-based observational cohort study included adult patients who had undergone cardiac surgery in Australia between 2010 and 2019. Patient data were linked with a kidney replacement therapy registry to identify cohorts accurately and extract relevant data. Multivariable logistic regression estimated the risk of operative (30-day) mortality and other postoperative outcomes for long-term dialysis and functioning kidney transplant cohorts compared with each other and the general cardiac surgical population. RESULTS: Of 114,496 surgeries, 1241 were in patients receiving long-term dialysis and 298 for those with a kidney transplant. The mortality rate was highest for patients who had valve-with-coronary artery bypass grafting for patients undergoing dialysis (18.78 per 100 surgeries
95% CI, 13.37-25.25) and transplant recipients (14.00 per 100 surgeries
95% CI, 5.82-26.74). Dialysis-treated patients had higher adjusted odds of mortality (odds ratio [OR], 4.17
95% CI, 3.31-5.25) and all other measured outcomes than did the general population. Kidney transplant recipients had similarly elevated odds of mortality (OR, 3.52
95% CI, 2.16-5.72). CONCLUSIONS: Despite the younger age of the dialysis and transplant cohorts at surgery, operative mortality rates were higher, and the mortality rates for valve-with-coronary artery bypass grafting were 3.7- to 5-fold higher than those in the general population. Patients undergoing dialysis were a high risk for cardiac surgery, and the prognosis for kidney transplant recipients was similarly poor.