Incidence of acute kidney injury among patients with chronic kidney disease: a single-center retrospective database analysis

Background Acute kidney injury (AKI) is a serious complication among hospitalized individuals and is closely associated with chronic kidney disease (CKD). Methods This retrospective cohort study evaluated the incidences of AKI according to CKD stage at Kochi Medical School hospital during 1981-2011. AKI was defined and staged according to the kidney disease improving global outcomes criteria, using serum creatinine levels. Results We analyzed data from 122,653 Japanese patients (57,105 men, 46.6 %). The incidence of AKI was 7.8 % (95 % confidence interval 7.7-8.0 %). Compared to nonAKI patients, patients with stage 1-2 AKI were more likely to be men. Patients with stage 1-2 AKI were significantly older than non-AKI or stage 3 AKI patients. The incidences of AKI were 6.7, 5.9, 10.4, 18.4, 30.0, and 48.8 % among individuals with estimated glomerular filtration rates of C90, 60-89, 45-59, 30-44, 15-29, and <15 mL/min/1.73 m(2), respectively; these were significantly different from the incidence for the baseline eGFR. The proportions of inpatients with AKI exhibited step-wise increases with more severe pre-existing reduced kidney function, and the proportions among outpatients exhibited step-wise increases with milder pre-existing reduced kidney function. Conclusions CKD was a risk factor for AKI, and the incidence of AKI was positively associated with pre-existing reduced kidney function (CKD stage). We also found that the prevalence of AKI at early-stage CKD among outpatients was higher than expected. We suggest that outpatients should be monitored for AKI, given its unexpected incidence in that population.