Incidence and consequences of acute kidney injury in kidney transplant recipients.

BACKGROUND

In the nontransplant setting, acute kidney injury (AKI) may lead to chronic kidney disease (CKD) and end-stage renal disease, but the epidemiology of AKI in transplant recipients has not been characterized. The purpose of this study was to determine the incidence and consequences of AKI in kidney transplant recipients outside the peritransplant period and unrelated to acute rejection.

STUDY DESIGN

Retrospective longitudinal cohort study.

SETTING & PARTICIPANTS: 27,232 adult Medicare-insured transplant recipients with transplant survival of 6 months or longer in the US Renal Data System in 1995-2000.

PREDICTORS

International Classification of Diseases, Ninth Revision, Clinical Modification (ICD-9-CM) hospital discharge diagnostic codes were used to identify AKI during the first 3 posttransplant years.

OUTCOMES

Transplant loss from any cause, mortality (death with a functioning transplant), and death-censored transplant loss.

MEASUREMENTS

Estimated glomerular filtration rate calculated by the MDRD (Modification of Diet in Renal Disease) Study equation 6 months posttransplant.

RESULTS

3,066 (11.3%) patients had 4,181 hospitalizations with AKI, of which 14.8% required dialysis therapy. The incidence of AKI more than doubled during the study, and AKI was more frequent in patients with lower levels of transplant function. AKI was associated independently with increased risk of transplant loss from any cause (HR, 2.74; 95% CI, 2.56-2.92), death with a functioning transplant (HR, 2.36; 95% CI, 2.14-2.60), and death-censored transplant loss (HR, 3.17; 95% CI, 2.91-3.46). However, AKI-associated risks paradoxically were higher in patients with earlier CKD stage.

LIMITATIONS

Because of the limited sensitivity of ICD-9-CM codes for non-dialysis-requiring AKI events, the overall incidence of AKI likely is underestimated in this study.

CONCLUSIONS

We conclude that AKI is increasingly common and associated with transplant failure and death. Later CKD stage increases the risk of AKI, but AKI-associated risks of transplant failure were greater in those with higher levels of kidney function (earlier CKD stage).