Kidney Tubule Dysfunction and Injury and the Long-Term Risk of Acute Kidney Injury Following Cardiac Artery Bypass Graft Surgery

Objective Determine whether urine biomarkers of kidney tubule dysfunction and injury are associated with future-term risk of post-CABG AKI. Design Nested cohort study using data from the REasons for Geographic And Racial Differences in Stroke (REGARDS) study. Setting A national, population-based, longitudinal cohort study of 30,239 U.S. adults aged ≥45 years. Participants We included all 760 participants who underwent CABG surgery. The final cohort included 394 participants after exclusion for a history of dialysis or kidney transplant at admission (n=3), illegible chart data (n=346), missing laboratory data (n=15) or underwent a cardiac procedure mislabeled as CABG (n=2). Exposures Using spot urine obtained at enrollment, an average of 5.5 years before CABG surgery, we measured biomarkers of kidney tubule dysfunction (urine alpha-1 microglobulin [A1M], uromodulin [UMOD] and epidermal growth factor [EGF]) and injury (kidney injury molecule-1 [KIM-1]). Main Outcomes AKI development following surgery, defined as an increase in serum creatinine ≥0.3 mg/dL from 48 hours prior to CABG to end of hospitalization. Results Of 394 eligible participants who underwent CABG (mean age 66, 29% female, 20% Black), 176 (45%) experienced post-operative AKI. Higher baseline urine A1M was associated with higher odds of AKI (adjusted OR 1.34 per 2-fold higher A1M, 95% Confidence Interval (CI): 1.00–1.80). Higher urine UMOD was associated with lower odds of AKI (adjusted OR 0.77 per 2-fold higher UMOD, 95% CI 0.62–0.95). Higher EGF showed a non-significant tendency towards lower odds of AKI (adjusted OR 0.79 per 2-fold higher EGF, 95% CI 0.59-1.05). KIM-1 was not associated with AKI (adjusted OR 0.92 per 2-fold higher KIM-1, 95% CI 0.77– 1.10). Conclusions Select biomarkers of tubule dysfunction, but not injury, measured when patients were at a stable baseline, are associated with future AKI after CABG. These markers of kidney dysfunction may offer a strategy for identifying individuals vulnerable to AKI after CABG.