Outpatient acute kidney injury (AKI), defined as AKI not requiring hospital admission, is more common than hospital AKI and is associated with an increased risk of death and renal events, investigators reported.
In a retrospective study, a team at the University of Minnesota in Minneapolis led by Paul E. Drawz, MD, found that outpatient AKI was associated with a significant 90% increased risk of death and 33% increased risk of renal events compared with the absence of AKI, after adjusting for potential confounders.
For the study, Dr Drawz and his collaborators defined outpatient AKI as a 50% increase in serum creatinine compared with baseline. They defined a renal event as a decrease in estimated glomerular filtration rate (eGFR) to less than 30 mL/min/1.73 m2 on at least 2 measurements with at least a 50% decline from the last value during an 18-month exposure period.
“The findings of this study reveal the significant consequences of AKI in the outpatient setting,” the investigators stated in a report published online ahead of print in Nephrology Dialysis Transplantation. “This burden is managed primarily in primary care clinics and efforts should now focus on prevention, early detection and rapid intervention. Unfortunately, evidence on how and where to focus these efforts is limited.”
Patients who recovered from outpatient AKI had a significant 2.1-fold increased risk of death and 73% increased risk of a renal event compared with patients who had no AKI, after adjustment for potential confounders. Patients who did not recover from outpatient AKI had a significant 71% increased risk of death, but they were not at increased risk for a renal event.
“Patients with AKI without recovery may have actually had a period of rapid decline in renal function rather than an acute isolated event,” Dr Drawz’s team explained. “It is possible that AKI poses a greater risk for adverse outcomes than a sustained decline in renal function.”
The study included 384,869 eligible adult patients receiving primary care from a large health system in Minnesota. The overall cohort had a mean age of 45.9 years. Patients with any outpatient AKI were older than those with no AKI (mean 60 vs 52.5 years).
All patients had at least 1 serum creatinine measurement available. During the 18-month exposure period, outpatient AKI occurred in 1.4% of patients, whereas hospital AKI occurred in only 0.3%. During an average follow-up period of 5.3 years, the overall mortality rate for the cohort was 3.2%.
“Our study is the most comprehensive analysis of outpatient AKI and is the first American cohort,” the authors noted.
The study’s size, length of follow-up, and robust comparator arm are among its strengths, as well as the availability of comprehensive clinical data that allowed for adjustment of potential confounders and assessment of multiple important outcomes. Limitations of the study include its retrospective and observational design.
Leither MD, Murphy DP, Bicknese L, et al. The impact of outpatient acute kidney injury on mortality and chronic kidney disease: a retrospective cohort study. Nephrol Dial Transplant. 2018; published online ahead of print.