Kidney Tubule Secretion and AKI After Cardiac Surgery

Introduction: Endogenous measures of impaired kidney tubule secretion are associated with kidney function decline. Whether they associate with future acute kidney injury (AKI) risk is unclear. Methods: In 397 participants of the Reasons for Geographic and Racial Differences in Stroke study who underwent coronary artery bypass graft (CABG) surgery (mean age: 66 years, 29% female), we examined the association of a summary secretion score of 11 endogenous secretion markers (measured at a median 5.5 years before CABG) with AKI risk following CABG, adjusting for confounders including estimated glomerular filtration rate (eGFR) and albuminuria. Results: A total of 177 participants developed AKI (≥ 0.3 mg/dl or 1.5× creatinine increase) following CABG. Individuals who developed AKI were older, more likely to be men, have diabetes, lower eGFR and greater albuminuria at the baseline visit. In models adjusted for age, sex, race, urine creatinine, time from baseline to CABG, diabetes, hypertension, and body mass index, a higher (signifying better) secretion score was associated with lower risk of AKI (risk ratio [RR] comparing 4th to 1st quartile: 0.49, 95% confidence interval [CI]: 0.32–0.74). The results did not meaningfully differ after further adjusting for eGFR and albuminuria (RR: 0.58, 95% CI: 0.38–0.89), or when secretion score was analyzed as a continuous variable (RR per 1 SD higher score: 0.85, 95% CI: 0.71–1.01). Associations were stronger in women (RR: 0.75, 95% CI: 0.59–0.95) than men (RR: 0.89, 95% CI: 0.69–1.16) in fully adjusted models (P_interaction = 0.01). Conclusion: In community-based adults, greater estimated tubular secretion at times of relative health is associated with lower risk of AKI following CABG.