We evaluated whether immediate postoperative urine dipstick occult blood after on-pump cardiac surgery could serve as an early indicator of high-risk cardiac surgery-associated acute kidney injury (CSA-AKI). This single-center retrospective study included 11,782 adult patients undergoing elective on-pump cardiac surgery (2018–2024), excluding those with preoperative chronic kidney disease (CKD, stage 3–5), positive preoperative urine occult blood, or postoperative microscopic hematuria. The primary outcome was any-stage CSA-AKI within 7 days after surgery. Multivariable logistic regression was used to evaluate the independent association between immediate postoperative urine occult blood and CSA-AKI. The predictive value was assessed by C-index, the net reclassification improvement index, and integrated discrimination improvement. The goodness-of-fit of models was evaluated through Akaike information criterion, Bayesian information criterion and likelihood ratio test. CSA-AKI occurred in 32.8% of patients, rising progressively across urine occult blood categories from 28.8% (negative group) to 37.9% (3 + group). After multivariable adjustment, 3 + urine occult blood was independently associated with higher odds of any-stage CSA-AKI (adjusted odds ratio aOR, 1.630; 95% confidence interval CI, 1.463–1.817; P < 0.001) and early CSA-AKI within 48 h (aOR, 1.692; 95% CI, 1.513–1.889; P < 0.001). Both 2 + and 3 + urine occult blood were independently associated with stage 2–3 CSA-AKI. Integrating urine occult blood into a clinical risk model that included established CSA-AKI predictors yielded a modest improvement in prognostic prediction and model fit. Immediate postoperative urine dipstick occult blood positivity was independently associated with an increased risk of CSA-AKI. As a simple and easily available biomarker, it may serve as an early indicator to identify patients at high risk of CSA-AKI in this selected cohort of adult patients undergoing elective on-pump cardiac surgery. Because direct markers of hemolysis or urinary heme proteins were not measured, the underlying biological mechanisms remain uncertain and require prospective validation.
Zhang et al. (Mon,) studied this question.