Role of renal arterial resistive index (RI) in obstructive uropathy

To determine the diagnostic accuracy of renal arterial resistive index on doppler ultrasound in patients with acute renal colic to diagnose obstructive uropathy taking non-enhanced helical computed tomography as the gold standard.

The descriptive study, conducted at the Radiology Department of Pakistan Naval Ship Shifa Hospital, Karachi, from October 10, 2010 to July 17, 2011, comprised 160 patients referred from the Emergency Department with complaint of unilateral renal colic. Ultrasound was carried out. Subsequently, computed tomography scan of kidney, ureter and bladder was performed. Data was collected on prescribed proforma and analysed using SPSS 19.

By taking the resistive index value of > 0.70 as a discriminatory level for obstruction, the overall sensitivity of the index was 76.23% and specificity was 88.13%. The positive predictive values of the index in patients with obstructive uropathy was 91.6%, and negative predictive value was calculated to be 68.42%. The diagnostic accuracy of the test was 80%.

Duplex Doppler ultrasound can detect acute renal obstruction with sensitivity of approximately 77%. However, ultrasound is an operator-dependent examination, and the results are much affected by patient body habitus.