Resistive index in renal colic: a prospective study

Abstract

Objective To study the role of Doppler ultrasonography (DU) in the diagnosis of acute unilateral renal obstruction. Patients and methods In all, 117 patients with suspected renal colic were evaluated by intravenous urography (IVU) and DU, with determination of the resistive index (RI) and the difference between the RI of ipsilateral and contralateral kidneys (ΔRI). RI and ΔRI were considered positive with values of ≥0.70 and ≥0.06, respectively. IVU results were considered the ‘gold standard’ with which renal DU findings were compared. Results IVU showed both kidneys to be normal in 49 patients and unilateral ureteric obstruction with a normal contralateral kidney in 68. The mean (sd) RI was 0.73 (0.05) in 68 obstructed kidneys, significantly higher than the mean RI of 0.64 (0.05) in 166 normal kidneys (PPn=42) had significantly higher values of RI and ΔRI than obstructed kidneys without delayed filling (n=26). The RI and ΔRI were more sensitive in the former group. Among patients with obstruction, the RI did not relate to the time of delay of filling with contrast medium, the duration of renal colic or the level of ureteric obstruction. Conclusions Renal DU is a sensitive and highly specific test that can contribute significantly to the diagnosis of acute unilateral renal obstruction. It can replace the IVU, particularly in situations where IVU is undesirable.