Diagnostic accuracy of doppler-derived renal ultrasound parameters for predicting acute kidney injury after cardiac surgery: a systematic review and meta-analysis.

Abstract

Background: Acute kidney injury (AKI) is a frequent and clinically significant complication following cardiac surgery. Doppler-derived renal ultrasound parameters-including the renal resistive index (RRI), semiquantitative power Doppler ultrasound (PDU) scales, and intrarenal venous flow (IRVF)-have been proposed as early, noninvasive predictors of postoperative AKI, but their diagnostic accuracy in this setting remains uncertain.

Methods: We conducted a systematic review of diagnostic test accuracy studies evaluating RRI, PDU, or IRVF for predicting AKI within 7 days after cardiac surgery in adult intensive care unit patients. MEDLINE, Embase, Cochrane CENTRAL, Scopus, Web of Science, and clinical trial registries were searched through June 2025. Sensitivity, specificity, diagnostic odds ratio (DOR), and area under the receiver operating characteristic curve (AUC) were extracted or calculated. Meta-analysis was performed for RRI using hierarchical bivariate models; IRVF and PDU were summarized descriptively due to limited studies and heterogeneity.

Results: Fourteen studies comprising 1,204 patients were included (12 RRI, 3 IRVF, 1 PDU). RRI thresholds between 0.71 and 0.74 demonstrated the highest diagnostic performance (AUC range 0.72-0.93). IRVF showed modest discrimination (AUC 0.62-0.66). Evidence for PDU was limited to one study. Substantial clinical and methodological heterogeneity was observed and overall certainty of evidence ranged from low to moderate.

Conclusions: Among Doppler-derived renal ultrasound parameters, RRI appears to have the most consistent diagnostic accuracy for predicting AKI after cardiac surgery. However, methodological heterogeneity, the limited number of studies, and the low-to-moderate certainty of the evidence preclude definitive clinical recommendations. Prospective multicenter validation studies with standardized protocols and prespecified thresholds are warranted.