ACUTE VERSUS CHRONIC KIDNEY DISEASE: UTILITY OF SHEAR WAVE ELASTOGRAPHY FOR ASSESSING CHRONICITY AND PREDICTING RECOVERY OF RENAL FUNCTION

Patients frequently present with reduced kidney function and uncertain chronicity. Correctly distinguishing acute kidney injury (AKI) from chronic kidney disease (CKD) is crucial for management, prognosis, and resource allocation. Conventional methods rely on clinical history, biochemical markers, and renal imaging findings such as kidney size, cortical echogenicity, and corticomedullary differentiation. However, these parameters lack sensitivity, especially in early stages or in patients with no baseline creatinine. Renal biopsy remains the gold standard for assessing chronicity and fibrosis, but it is invasive, carries procedural risks, and is limited by sampling variability. Shear Wave Elastography (SWE) is a non-invasive ultrasound-based technique that quantifies tissue stiffness, which correlates with histologic fibrosis in various organs, including the liver and kidney.  However, data remain limited, especially in real-world clinical cohorts, and threshold values differentiating AKI from CKD are not well established. This study aimed to establish the diagnostic value of SWE in evaluating renal fibrosis, and predicting recovery of renal function.

This prospective study included patients who underwent renal biopsy due to renal dysfunction between September 2019 and September 2021. Participants were categorized into two groups: acute kidney injury (AKI) and chronic kidney disease (CKD) based on recovery of renal function. Patents showing partial to complete recovery were categorised as AKI. Exclusion criteria included patients with a BMI ≥ 23 kg/m², a kidney depth greater than 6 cm from the skin, or those unable to hold their breath during the SWE procedure. SWE was performed prior to the kidney biopsy and renal stiffness was expressed as kPa. After biopsy, renal fibrosis was assessed by renal pathologist, and was expressed histopathological chronicity score. The renal stiffness was correlated with histopathological chronicity score and recovery of renal function.

A total of 145 patients were included in the study, with 65% male and 35% female. AKI and CKD were diagnosed in 38.62% (n=56) and 61.38% (n=89) of patents, respectively. The mean histopathological chronicity scores were 2.20 ± 1.61 for AKI and 7.06 ± 1.71 for CKD (p < 0.001). The mean renal stiffness (kPa) was 17.95 ± 4.46 for AKI and 30.31 ± 7.12 for CKD (p < 0.001). A positive correlation was found between histopathological chronicity scores and renal stiffness (r = 0.697; n = 145; p < 0.001). The histopathological chronicity score has AUC 0.982 (95% CI: 0.964 –1.000, P < 0.001) with best cutoff value of 4.5 (sensitivity 97.8%; specificity 92.9%) for predicting nonrecovery of renal function. Similarly, the renal stiffness has AUC 0.933 (95% CI: 0.896 – 0.970, P < 0.001) with best cutoff value of 23.51 (sensitivity 82%; specificity 83.9%) for predicting nonrecovery of renal function.  

Renal stiffness measured by SWE, though inferior to histopathological chronicity score, still can effectively predict the extent of renal fibrosis. It may serve as a valuable non-invasive tool for predicting the potential the recovery of renal function and differentiating AKI from CKD, particularly in critical care settings.