Pre-operative proteinuria and post-operative acute kidney injury in noncardiac surgery: the NARA-Acute Kidney Injury cohort study

BACKGROUND: Little is known about the association between pre-operative proteinuria and post-operative acute kidney injury (AKI) in noncardiac surgery. METHODS: This is a retrospective cohort study. Adults who underwent noncardiac surgery under general anesthesia from 2007 to 2011 at Nara Medical University Hospital were included. Those with obstetric or urological surgery, missing data for analyses or pre-operative dialysis were excluded. Exposure of interest was pre-operative proteinuria, defined as (+) or more by dipstick test. The outcome variable was post-operative AKI, defined by Kidney Disease: Improving Global Outcomes criteria, within 1 week after surgery. Multivariable logistic regression analyses were performed. RESULTS: Among 5168 subjects, 309 (6.0%) developed AKI. Pre-operative proteinuria was independently associated with post-operative AKI, with an odds ratio (OR) 95% confidence interval (CI) of 1.80 (1.30-2.51). A sensitivity analysis restricted to elective surgery yielded a similar result. As proteinuria increased, the association with AKI became stronger OR (95% CI) 1.14 (0.75-1.73), 1.24 (0.79-1.95), 2.75 (1.74-4.35) and 3.95 (1.62-9.62) for urinary protein (+/-), (+), (2+) and (3+), respectively. Subgroup analyses showed proteinuria was especially associated with post-operative AKI among subjects with renin-angiotensin system inhibitors, other anti-hypertensives, hypoalbuminemia or impaired renal function (P for interaction = 0.05, 0.003, 0.09 or 0.02, respectively). CONCLUSIONS: In noncardiac surgery, pre-operative proteinuria was independently associated with post-operative AKI. Subjects with proteinuria should be managed with caution to avoid AKI peri-operatively.