# Renal Shear Wave Elastography for Differentiating Vasculitic and Non-Vasculitic Acute Kidney Injury

## TL;DR

Renal shear wave elastography can help distinguish between vasculitic and non-vasculitic acute kidney injury and may predict renal outcomes.

## Contribution

This study is the first to demonstrate the diagnostic utility of renal elastography in acute kidney injury and its potential prognostic value in IgAVN.

## Key findings

- Vasculitic AKI showed significantly higher renal cortical stiffness compared to non-vasculitic AKI and healthy controls.
- Renal cortical stiffness had good diagnostic performance with an AUC of 0.86 for differentiating vasculitic from non-vasculitic AKI.
- Higher baseline stiffness in IgAVN was associated with worse one-year renal outcomes.

## Abstract

Background/Objectives: Early identification of vasculitic acute kidney injury (AKI) is crucial for timely immunosuppression and improved renal outcomes; however, noninvasive adjunctive diagnostic tools remain limited. Renal elastography, a noninvasive technique that quantifies renal cortical stiffness, has been primarily investigated in chronic kidney disease, whereas evidence in acute kidney injury is scarce. This study aimed to evaluate the diagnostic utility of renal shear wave elastography for differentiating vasculitic from non-vasculitic AKI and to explore the association between baseline renal cortical stiffness and vasculitic renal outcomes. Materials and Methods: This prospective observational study included three groups: vasculitic AKI, non-vasculitic AKI, and healthy controls. Renal cortical stiffness was measured at admission using two-dimensional shear-wave elastography (2D-SWE) by radiologists blinded to clinical information. After clinicopathological confirmation of definitive diagnoses, between-group comparisons were performed and the diagnostic performance of elastography was evaluated. Additionally, in a biopsy-confirmed immunoglobulin A vasculitis nephritis (IgAVN) cohort (n = 12), baseline elastography measurements were examined in relation to one-year renal outcomes to explore potential prognostic associations. Results: The vasculitic AKI group exhibited significantly higher mean renal cortical stiffness values (9.5 ± 1.9 kPa) compared with both healthy controls (5.53 ± 0.92 kPa) and the non-vasculitic AKI group (6.61 ± 1.89 kPa) (both p < 0.01). Mean renal cortical stiffness demonstrated good diagnostic performance for distinguishing vasculitic from non-vasculitic AKI (AUC 0.86, 95% CI 0.73–0.97), with an optimal threshold of 6.79 kPa yielding 91% sensitivity and 72% specificity. In the prospective one-year follow-up of the IgAVN subcohort (n = 12), patients with unfavorable renal outcomes tended to have higher baseline renal cortical stiffness compared with those with favorable outcomes [median (min–max), 11.2 (10.8–13.3) vs. 9.1 (5.6–11.2), p = 0.046]. Conclusions: These findings suggest that renal elastography may aid in distinguishing vasculitic from non-vasculitic acute kidney injury and may provide exploratory information on the relationship between baseline cortical stiffness and renal outcomes in IgAVN.