Outpatient Acute Kidney Injury Increases Risk of Mortality and Chronic Kidney Disease

Abstract

Introduction: Limited data exist regarding outcomes of patients with outpatient acute kidney injury (AKI). To determine whether outpatient AKI is associated with increased mortality and chronic kidney disease (CKD), we conducted a retrospective cohort study utilizing an electronic health record in Minnesota. Methods: All adult patients receiving primary care through Fairview Health Services were included. All outpatient Cr values during an 18 month exposure period were used to define five comparator groups as follows: No outpatient AKI (reference group), outpatient AKI with recovery, outpatient AKI without recovery, outpatient AKI without repeat Cr, or no Cr. A Cox proportional hazard model was utilized to assess whether outpatient AKI was associated with an increase in mortality, CKD stage 4 and secondary outcomes including hospitalization and recurrent AKI. Results: The cohort consisted of 384,869 patients and 51% had at least one Cr measured during the exposure period. Outpatient AKI occurred in 1.4% of patients during the 18 month exposure period and 37.8% recovered while 26.5% had no repeat Cr. Mortality was 3.2% over an average follow-up of 5.3 years. Outpatient AKI was associated with an increased risk of mortality (aHR 1.90, 95% CI 1.76-2.06) and CKD stage 4 (aHR 1.33, 95% CI 1.11-1.59) including those that recovered from their AKI (mortality aHR 2.15, 95% CI 1.91-2.41; CKD aHR 1.73, 95% CI 1.37-2.19) and in those with stage 1 AKI (mortality aHR 1.90, 95% CI 1.74-2.07; CKD aHR 1.34, 95% CI 1.10-1.62). Outpatient AKI was also associated with with an increased risk of hospitalization (aHR 1.71, 95% CI 1.63-1.79), hospital AKI (aHR 2.14, 95% CI 1.93-2.37), and recurrent outpatient AKI (aHR 2.75, 95% CI 2.57-2.93). Conclusion: Outpatient AKI is common and is a risk factor for death, CKD, hospitalization, and recurrent AKI, including those with stage 1 AKI and those that recover.