Association between the recurrence period of acute kidney injury and mortality: a single-centre retrospective observational study in Japan

OBJECTIVES: Recurrent acute kidney injury (AKI) is a recognised risk factor for mortality. However, it is unclear whether the period until AKI recurrence may have a major factor on patient outcome or not. To explore this issue, we (1) framed the hypothesis that early recurrence increases the risk of mortality and (2) evaluated the prognosis of recurrent AKI cases by setting 21 days as the cut-off period. METHODS: All studied cases were admitted and followed up at the Kanazawa University Hospital (Kanazawa, Japan) between 1 November 2006 and 31 October 2007. In total, 21 939 patients were retrospectively evaluated in their recurrences of AKI for 2 years and followed up until 31 October 2016. Risks for death were evaluated by the recurrences of AKI (Analysis 1). Patients who developed AKI recurrence before 21 days were defined as the early-recurrence group and the remaining cases as the late-recurrence group. Risks for death were evaluated by the two groups (Analysis 2). RESULTS: 510 patients (2.3%) developed the first AKI. Of these, 151 developed recurrent AKI within 2 years. The number of early-recurrence cases was 44 and that of non-recurrence or late-recurrence was 357. A total of 196 cases (38.4%) died, and higher risk for death was observed in the recurrent AKI group (Analysis 1; p=0.015, log-rank test). We found that the rate of all-cause mortality was higher in the early-recurrence group involving 33.8 deaths per 100 person-years, whereas the non-recurrence or late-recurrence group included only 6.2 deaths per 100 person-years (Analysis 2; p<0.001, log-rank test). CONCLUSIONS: Patients experiencing recurrent AKI before 21 days from the first AKI clearly showed a relatively poor prognosis. Evidently, careful follow-up for at least 21 days after AKI would be highly useful to detect a recurrence event, possibly leading to a better prognosis after AKI.