<b>DIAGNOSTIC ACCURACY OF RENAL ARTERY RESISTIVE INDEX IN DIAGNOSING OBSTRUCTIVE UROPATHY TAKING NON-ENHANCED CT AS GOLD STANDARD</b>

Background: Obstructive uropathy is a major cause of acute and chronic renal failure, which requires quick and precise diagnosis. Renal Artery Resistive Index (RI) measured using Doppler ultrasound is a non-invasive, radiation-free technique. The purpose of this research is to identify the accuracy of the renal artery resistive index (RI) in identifying obstructive uropathy based on NECT as the gold standard at a tertiary care hospital in Islamabad. Methods: A total of 225 subjects of both genders with age between 18-80 years who presented with the symptoms of acute renal colic, were enrolled for this cross-sectional validation study using the non-probability consecutive sampling technique. Study was done at the PAF Hospital Radiology Department, Islamabad, between April 15, 2024, and December 15, 2024. Color Doppler Ultrasound was performed to every participant to measure intra-renal artery RI and subsequent NECT KUB was carried out. Renal artery RI value more than 0.70 was regarded as positive obstruction. Diagnostic indices such as Sensitivity, specificity, and Area Under the Curve (AUC) were determined. Results: The mean age of the participants was 40.72±13.73 years. Non-enhanced CT established the presence of obstructive uropathy in 31.6% (n=71) of cases. The renal artery RI demonstrated a sensitivity and specificity of 87.32% and 88.31% respectively; while, positive predictive value (PPV) and negative predictive value (NPV) were 77.5% and 93.79%. The overall diagnostic accuracy was 88.00%. Receiver Operating Characteristic (ROC) analysis revealed an excellent discriminative power with an AUC of 0.884 (95% CI: 0.837–0.931). Conclusion: Renal Artery Resistive Index is a very reliable diagnostic tool that is used to detect the presence of obstructive uropathy at an early stage. Its decent NPV and AUC make it a valuable non-invasive substitute to non-enhanced CT, especially to use it in the triage of patients and to reduce radiation dose in clinical practice.