Resistive index of the solitary kidney: a clinical study of normal values.

PURPOSE: We studied changes in the renal resistive index (RI) of the remaining kidney after live donor nephrectomy. MATERIALS AND METHODS: The study included 24 healthy live kidney donors (14 males and 10 females) with a mean age of 42 years. After donor evaluation Doppler ultrasound was done of the 2 kidneys the day before nephrectomy with RI measurement of each kidney. After nephrectomy the RI of the remaining kidney was measured on days 2, 4, 6, 8 and 10, and then at weeks 2, 3, 6 and 12. Mean RI of the remaining kidney before nephrectomy was compared to values at different time points after nephrectomy. Changes in the RI of the remaining kidney were screened at the followup time points. RESULTS: There was no difference between the mean RIs of the right and left kidneys before nephrectomy (0.67 +/- 0.04 and 0.67 +/- 0.04, respectively). The RI of the remaining kidney increased from 0.67 +/- 0.04 before nephrectomy to 0.71 +/- 0.06 on day 2 after nephrectomy, which was significantly different (p <0.0001). The mean RI increase of the remaining kidney on day 2 was 0.05 +/- 0.03. The RI of the remaining kidney remained almost stable on days 4, 6, 8, and 10, and also at week 2. Comparison between the mean RI at weeks 2 (0.72 +/- 0.05) and 3 (0.73 +/- 0.05) showed a further increase of significant value (p <0.0001). The mean RI remained stable at weeks 6 (0.73 +/- 0.05) and at 12 (0.73 +/- 0.05). CONCLUSIONS: The RI of the remaining kidney significantly increases after nephrectomy of the contralateral kidney. Therefore, an RI value of 0.7 is not suitable to diagnose a pathological condition in a solitary kidney in adults.

Recoverability of renal function after relief of acute complete ureteral obstruction: clinical prospective study of the role of renal resistive index.

OBJECTIVES: To study the values of the renal resistive index (RI) before and at different points after relief of obstructive anuria and to correlate these values with the corresponding values of serum creatinine and with the recovery of renal function after release of obstruction. METHODS: A total of 32 consecutive patients with obstructive anuria were prospectively evaluated by measurement of RI before drainage and at 3 days, 1 week, 2 weeks, and 4 weeks after drainage. Serum creatinine was measured at all points of the RI examination. Moreover, RI was measured in an age and sex-matched control group of 24 consecutive healthy donors and volunteers. RESULTS: The study included 40 obstructed and 48 normal kidneys. In the obstructed kidneys, the mean RI values decreased significantly from 0.78 +/- 0.05 before drainage to 0.70 +/- 0.09 at 3 days after drainage (P <0.001) with an additional significant reduction to 0.68 +/- 0.08 at 7 days after drainage (P <0.01) and stabilized thereafter. Serum creatinine decreased significantly from 8.4 +/- 4.4 mg/dL before drainage to 4.7 +/- 3.8 mg/dL 3 days after drainage (P <0.001) and then to 3.6 +/- 3.7 mg/dL 7 days after drainage (P <0.001) and stabilized thereafter. The correlation between the RI and serum creatinine at the overall points of measurement was good. Obstructed kidneys were classified into two groups according to the recovery of renal function after obstruction relief: those that showed significant improvement of serum creatinine (24 kidneys, group 1) and those with no significant improvement of serum creatinine (16 kidneys, group 2). In group 1, the difference between the mean RI values before and after drainage was statistically significant (0.78 +/- 0.05 versus 0.64 +/- 0.06, P <0.001); in group 2, the difference between the before and after drainage RI values was not significant (0.781 +/- 0.040 versus 0.779 +/- 0.039). The mean RI of the normal kidneys was 0.66 +/- 0.04. A comparison between the mean RI values of the control group and the mean RI values of the obstructed patients after drainage showed no significant difference in group 1; markedly higher values were noted in group 2 at all points after drainage. CONCLUSIONS: In the setting of acute complete renal obstruction, the RI has a good positive correlation with serum creatinine. Recovery of renal function could not be predicted from the changes in RI before obstruction release. However, a reversal of a previously elevated RI could be used as an early indicator that renal function recovery is likely.