Association between AKI, recovery of renal function, and long-term outcomes after hospital discharge

Abstract

Background and objectives: This study aimed to determine if recovery of kidney function after AKI modifies the association between AKI during hospitalization and adverse outcomes after discharge.

Design, setting, participants, & measurements: The effect of renal recovery after AKI was evaluated in a population-based cohort study (n=190,714) with participants identified from a provincial claims registry in Alberta, Canada, between November 1, 2002 and December 31, 2007. AKI was identified by a two-fold increase between prehospital and peak in-hospital serum creatinine (SCr). Recovery was assessed using SCr drawn closest to 90 days after the AKI event. All-cause mortality and a combined renal outcome of sustained doubling of SCr or progression to kidney failure were evaluated.

Results: Overall, 3.7% of the participants (n=7014) had AKI, 62.7% of whom (n=4400) survived 90 days. In the 3231 patients in whom recovery could be assessed over a median follow-up of 34 months, 30.8% (n=1268) of AKI survivors died and 2.1% (n=85) progressed to kidney failure. Participants who did not recover kidney function had a higher risk for mortality and adverse renal outcomes when AKI participants who recovered to within 25% of baseline SCr were used as the reference group (adjusted mortality hazard ratio (HR), 1.26; 95% confidence interval, 1.10, 1.43) (adjusted renal outcomes HR, 4.13; 95% confidence interval, 3.38, 5.04). Mortality HR was notably higher when participants failed to recover within 55% of baseline.

Conclusions: Renal recovery after AKI is associated with a lower risk of death or adverse renal outcomes after hospital discharge.

Figure 1.

Study flowchart. In this figure, ESRD and doubling SCr are mutually exclusive groups. If a participant had both ESRD and sustained doubling SCr, we classified him or her to the ESRD group. SCr, serum creatinine.

Figure 2.

Renal recovery after AKI is associated with improved patient and renal survival. (A) Adjusted curves for survival in AKI survivors by recovery status (recovery defined as within 25% of baseline). (B) Adjusted curves for renal survival in AKI survivors by recovery status (recovery defined as within 25% of baseline). Adjusted for age, sex, myocardial infarction, peripheral vascular disease, cerebrovascular disease, congestive heart failure, uncomplicated diabetes, complicated diabetes, nondermatologic malignancy, baseline estimated GFR (by 5 ml/min per 1.73 m² increments), acute dialysis during hospitalization, primary diagnostic code for hospitalization, and Canadian Institute for Health Information resource intensity weight.

Figure 3.

Identification of thresholds for significant renal recovery in relation to patient and renal survival. (A) Adjusted HRs for mortality of each mutually exclusive group during the follow-up period (recovery to within 5% is reference group) (n=3188). (B) Adjusted hazard ratios for ESRD/sustained doubling SCr of each mutually exclusive group during follow-up period (recovery to within 5% is reference group) (n=3188). Both A and B were adjusted for age, sex, myocardial infarction, peripheral vascular disease, cerebrovascular disease, congestive heart failure, uncomplicated diabetes, complicated diabetes, nondermatologic malignancy, baseline estimated GFR (by 5 ml/min per 1.73 m² increments), acute dialysis during hospitalization, primary diagnostic code for hospitalization, and Canadian Institute for Health Information resource intensity weight. Analysis excludes 43 participants who started dialysis during the recovery assessment period. SCr, serum creatinine; HR, hazard ratio; 95% CI, 95% confidence interval.