Prospective evaluation of interobserver variability of the hydronephrosis index and the renal resistive index as sonographic examination methods for the evaluation of acute hydronephrosis

OBJECTIVE To confirm the reliability of assessements of the renal resistive index (RRI) and the hydronephrosis index (HI) comprising two sonographic techniques providing additional information in patients with acute renal colic. PATIENTS AND METHODS Sonographic measurement of hydronephrosis and assessment of common clinical criteria was performed in 22 consecutive patients presenting with unilateral stone-related renal colic. RRI and HI were separately recorded by two investigators within a prospective study. Interobserver agreement and comparison of sonographic with computed tomography (CT) findings were assessed with the Cohen's kappa statistic (kappa) for attributive ordinal characteristics and Spearman's rank correlation/rho (rho) for attributive metric characteristics. RESULTS There was a significant correlation between HI and the sonographically-evaluated grade of hydronephrosis, although not between RRI and the grade of hydronephrosis. For all procedures (RRI, HI, sonography and CT), significant differences between the symptomatic and the asymptomatic kidney were assessed. Interobserver agreement was excellent for the grade assessment of hydronephrosis by conventional sonography (kappa = 0.82; P < 0.001), good to very good for HI (rho = 0.60; P = 0.003) and acceptable to good for RRI (rho = 0.49; P = 0.021). CONCLUSIONS The RRI and HI methods are both easily practicable as stageless examination methods in patients presenting with stone-related renal colic, and both also reliably distinguish between obstruction and non-obstruction. Exact thresholds for both methods must still be defined based on further successive studies. Additionally, changes of values under medical expulsive therapy and correlation with the functional status of the obstructed kidney remain to be examined.