Correlation between renal resistive index (RI) and nonenhanced CT in acute renal colic: How reliable is RI in distinguishing obstruction?

. The purpose of this study was to determine the sensitivity of renal color Doppler sonography in differentiating obstructive and nonobstructive urinary calculi in patients with acute renal colic and to compare findings with nonenhanced helical computed tomography (CT). Methods. Sixty-five patients referred to the emergency department with acute renal colic underwent nonenhanced CT and renal resistive index (RI) measurement with color pulsed Doppler sonography within 8 to 10 hours of the onset of the symptoms. Computed tomographic evaluation was based on the detection of urolithiasis and classification according to location and the presence of obstruction. The mean RI of each kidney and the difference between the mean RI (ΔRI) of both kidneys were calculated and compared with CT findings. Results. A total of 164 stones were identified. Computed tomography revealed obstruction in 33 patients. Mean RI values for the obstructive and nonobstructive groups were 0.64 and 0.63, respectively. Mean ΔRI values were 0.01312 and 0.01000 in the obstructive and nonobstructive groups. The differences in the mean RI and ΔRI for the patients with and without obstruction were statistically insignificant (P = .73). No significant relationship was found between the RI values, calculus location, and degree of obstruction.