Resistive index in renal colic: a prospective study

To study the role of Doppler ultrasonography (DU) in the diagnosis of acute unilateral renal obstruction.

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 (deltaRI). RI and deltaRI were considered positive with values of > or = 0.70 and > or = 0.06, respectively. IVU results were considered the 'gold standard' with which renal DU findings were compared.

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 (P<0.001). The deltaRI in patients with unilateral obstruction was significantly higher than that in patients with both kidneys normal, at 0.09 (0.05) and -0.001 (0.02), respectively (P<0.001). For all the patients, RI was sensitive in 77% and specific in 83%, and deltaRI was sensitive in 88% and specific in 98%. Obstructed kidneys showing delayed pelvicalyceal filling with excretion of contrast medium (n=42) had significantly higher values of RI and deltaRI than obstructed kidneys without delayed filling (n=26). The RI and deltaRI 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.

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.