Hypothesis / aims of study
Urological interventions for urolithiasis such as extracorporeal shock wave lithotripsy (ESWL), percutaneous nephrolithotomy (PCNL), and ureteroscopy (URS) can induce varying degrees of renal injury. Traditional kidney function tests, such as serum creatinine and eGFR, may fail to detect changes in the early postoperative period. In contrast, urinary biomarkers and Doppler-derived renal resistive index (RRI) could reveal early, subclinical renal injury, providing a more sensitive assessment including tubular damage, inflammation, and vascular stress, of renal response to these procedures.
Aim:
To evaluate early renal injury following urological interventions for urolithiasis by assessing urinary NGAL, KIM-1, and IL-18 levels in conjunction with renal resistive index (RRI).
Study design, materials and methods
Methods:
A prospective controlled study was conducted on 188 patients, who were divided into three groups: ESWL (n = 63), PCNL (n = 60), and URS (n = 65). Urinary NGAL, KIM-1, and IL-18 levels were measured at baseline and at 6 and 12 hours after the procedures using ELISA. The renal resistive index (RRI) was assessed by Doppler ultrasound at baseline and 6 hours post-intervention. Serum creatinine and estimated glomerular filtration rate (eGFR) were evaluated at baseline and 6 days after the procedures.
Results
Results:
Serum creatinine levels showed a mild postoperative increase, most prominent following PCNL, yet remained within the normal physiological range in all groups. This change was accompanied by a modest but statistically significant decline in eGFR after PCNL compared with ESWL (p = 0.016) and URS (p = 0.012). Urinary NGAL peaked at 6 hours post-procedure in PCNL (p < 0.001) and ESWL groups (p < 0.001), while KIM-1 and IL-18 showed maximal elevations at 12 hours, particularly after PCNL. RRI values increased significantly post-PCNL and ESWL versus URS (p = 0.007), (p =0. 024) respectively.
Interpretation of results
Our study demonstrated that urinary IL-18 levels showed the greatest elevation at 12 hours following PCNL compared with URS and ESWL. Moreover, IL-18 levels in the ESWL group were also higher than those observed in the URS group. This increase likely reflects the release of pro-inflammatory cytokines, including IL-18 and other IL-1 family members[28], from damaged tubular cells and recruited leukocytes during PCNL, indicating a stronger inflammatory response and tubular stress associated with this procedure.In accordance with our findings Zorkin et al. who evaluated urinary IL-18 changes in children with urolithiasis following ESWL and observed a significant rise at 24 hours post-procedure [29].
The renal resistive index provides a real-time functional assessment of renal hemodynamics, reflecting vascular resistance and intrarenal perfusion, and thus complements structural indicators of renal injury. In the present study, we observed a significant increase in RRI following PCNL, followed by a moderate rise after ESWL, while only mild rise was detected after URS suggesting a lower hemodynamic burden associated with this intervention.
In line with our findings, a study from India reported a significant increase in RRI as early as 3 hours post-ESWL [13]. Additionally, a recent Egyptian study highlighted RRI as a reliable predictor of sepsis-associated AKI[31]. In contrast, a prospective study in a pediatric population (aged 2–17 years) found no significant changes in RRI following PCNL or URS, likely due to smaller stone burden and the greater regenerative capacity of pediatric kidneys[32].
Concluding message
PCNL and ESWL could induce measurable renal injury reflected by elevated urinary NGAL, KIM-1, IL-18, and increased RRI, while URS exerts a comparatively lesser effect. The combined assessment of urinary biomarkers and Doppler-derived RRI offers a sensitive, non-invasive approach for early detection and monitoring of procedure-related kidney injury.