Short- and Long-Term Repeatability of Intrarenal Resistive Index in the Pig

RATIONALE AND OBJECTIVES: To evaluate the short- and long-term repeatability (intraobserver variation) of the renal resistive index (RI) in a pig model. METHODS: Under standardized ambient conditions, short- and long-term repeatabilities were assessed by measuring the RI three consecutive times at 30-minute intervals in 14 pigs and twice 4 weeks apart in 6 pigs, respectively. Repeatability was judged according to predefined criteria, which included calculation of coefficients of variation (CVs) and repeatability coefficients combined with visual assessment and estimation of bias. RESULTS: Short-term repeatability was acceptable, having an average CV of 4.9% +/- 2.9% and of 6.1% +/- 4.7% in two comparisons, findings that were reiterated in the visual assessment. Long-term results were, however, less consistent, having an average CV of 8.1% +/- 6.1% and prominent scatter on the visual assessment graphs. CONCLUSIONS: In this study, RI measurements showed an acceptable short-term repeatability, whereas long-term results were less consistent. The components of error contributing to the modest long-term repeatability need to be investigated in studies of larger populations.