BACKGROUND Urolithiasis remains a major health problem worldwide. Patients with renal colic are 33% to 68.3% at risk of acute urinary obstruction (partial or complete) leading to hydroureteronephrosis. Our study was done to determine the sensitivity of the renal resistive index in diagnosing obstructive uropathy taking non-enhanced helical CT as the gold standard. MATERIALS AND METHODS This is an observational study done in Government Kilpauk Medical College Hospital and Government Royapettah Hospital, Chennai from August 2015 - March 2017. During the study period, patients with unilateral loin pain to emergency department were evaluated with bilateral colour Doppler Ultrasound and plain CT KUB reconstructed images. The Renal RI was calculated by subtracting the peak diastolic velocity from the peak. Renal RI > 0.7 was considered diagnostic of obstructive uropathy. Delta RI > 0.06 was taken as diagnostic of obstructive uropathy. The efficacy of these tests was determined by calculating specificity, sensitivity, positive predictive value, negative predictive value and accuracy. RESULTS RI was found to be < 0.7 in 96% (48%) of the 200 patients. Ureteric calculus was seen on CT scan in 32 (33.33%) of these patients. In 64 (67.7%) of these 96 patients, ureteric calculus was not seen on CT. The overall sensitivity of RI was 74.80% and specificity was 87.83%. The PPV of RI was 91.34% and NPV was 66.66%. The diagnostic accuracy of the test was 79.5%. Delta RI was found to be > 0.06 in 104 (52%) patients. Calculus was seen on CT scan in 97 (93.26%) of these 104 patients. In the remaining 7 (6.74%) of these, 104 patients' calculus was not seen on CT. Delta RI was found to be < 0.06 in 96 (48%) of the 200 patients. Calculus was seen on CT in 30 (31.25%). In 66 (68.75%) of these 96 patients, ureteric calculus was not seen on CT. By taking Delta RI value of > 0.06 as a discriminatory level for obstruction, the overall sensitivity of DRI was 76.37% and specificity was 90.41%. The PPV of Delta RI was 93.26% and NPV was 68.75%. The diagnostic accuracy of the test was 81.5%. CONCLUSION Renal RI is less sensitive in diagnosing acute ureteric obstruction, as RI has been shown to be influenced by various factors. If Delta RI is applied, sensitivity and specificity, positive predictive value, negative predictive value and accuracy in diagnosing complete ureteric obstruction will be increased.
