Resistance and pulsatility indices in acute renal obstruction

PURPOSE: The aim of this study was to evaluate the reliability of Doppler waveform alterations in diagnosing acute unilateral renal obstruction. METHODS: From December 1993 to January 1996, 54 patients with unilateral renal obstruction were prospectively examined by conventional and duplex Doppler sonography. Seventy-eight patients with nonrenal abdominal problems comprised the control group. Doppler signals were obtained from interlobar arteries and arcuate arteries at the corticomedullary junction. From the waveform analysis, we calculated resistance (RI) and pulsatility (PI) indices. We also used the differences in RI and PI between the 2 kidneys in the same examinee (delta RI and delta PI) for further statistical analysis. RESULTS: The mean RI and PI (+/- standard deviation) in the patients without renal impairment were 0.64 +/- 0.04 and 1.14 +/- 0.14, respectively. The mean delta RI and delta PI were 0.02 +/- 0.01 and 0.07 +/- 0.05, respectively. Both the RI and PI were significantly correlated with age (r = 0.74 and 0.69, respectively; p < 0.01). Acute renal obstruction significantly (p < 0.01) elevated the mean RI (0.72 +/- 0.04), delta RI (0.09 +/- 0.04), PI (1.42 +/- 0.17), and delta PI (0.33 +/- 0.18). Significant decreases in RI and delta RI were noted after relief of the obstruction. The best accuracy in diagnosing acute unilateral renal obstruction was achieved with the combination of delta RI > or = 0.06 and/or delta PI > or = 0.20, which had a sensitivity of 94% and specificity of 99%. CONCLUSIONS: Renal Doppler indices are reliable parameters in the sonographic diagnosis of acute unilateral obstructive uropathy.