The duration of acute kidney injury is an additional parameter to predict 1-year survival in very elderly patients

BACKGROUND: Acute kidney injury (AKI) is primarily defined and classified according to the magnitude of the elevation of serum creatinine (Scr). We aimed to determine whether the duration of AKI adds prognostic value in addition to that obtained from the magnitude of injury alone. METHODS: This retrospective study enrolled very elderly inpatients (≥75 years) in the Chinese PLA General Hospital from January 2007 to December 2018. AKI was stratified by magnitude according to KDIGO stage (1, 2, and 3) and duration (1–2 days, 3–4 days, 5–7 days, and >7 days). The primary outcome was the 1-year mortality after AKI. Multivariable Cox regression analysis was performed to identify covariates associated with the 1-year mortality. The probability of survival was estimated using the Kaplan–Meier method, and curves were compared using the log-rank test. RESULTS: In total, 688 patients were enrolled, with the median age was 88 (84–91) years, and the majority (652, 94.8%) were male. According to the KDIGO criteria, 317 patients (46.1%) had Stage 1 AKI, 169 (24.6%) had Stage 2 AKI, and 202 (29.3%) had Stage 3 AKI. Of the 688 study subjects, 61 (8.9%) with a duration of AKI lasted 1–2 days, 104 (15.1%) with a duration of AKI lasted 3–4 days, 140 (20.3%) with a duration of AKI lasted 5–7 days, and 383 (55.7%) with a duration of AKI lasted >7 days. Within each stage, a longer duration of AKI was slightly associated with a higher rate of 1-year mortality. However, within each of the duration categories, the stage of AKI was significantly associated with 1-year mortality. When considered separately in multivariate analyses, both the duration of AKI (3–4 days: HR=3.184; 95% CI: 1.733–5.853; P <0.001, 5–7 days: HR=1.915; 95% CI: 1.073–3.416; P=0.028; >7 days: HR=1.766; 95% CI: 1.017–3.065; P=0.043) and more advanced AKI stage (Stage 2: HR=3.063; 95% CI: 2.207–4.252; P <0.001; Stage 3: HR=7.333; 95% CI: 5.274–10.197; P <0.001) were independently associated with an increased risk of 1-year mortality. CONCLUSIONS: In very elderly AKI patients, both a higher stage and duration were independently associated with an increased risk of 1-year mortality. Hence, the duration of AKI adds additional information to predict long-term mortality.