Intrarenal Resistive Index after Renal Transplantation

Naesens et al. (Nov. 7 issue)1 published their findings of a well-conducted study looking at the relationship between intrarenal resistive indexes in renal allografts and allograft dysfunction. With regard to the protocol-specified measurements, higher resistive indexes were not associated with allograft dysfunction but were associated with older recipient age and increased mortality. After reading the article, my colleagues and I had a few questions and comments. First, what is the rationale for using a cutoff value of 0.80 to distinguish a lower resistive index from a higher resistive index and for treating the resistive index as a categorical variable when it is in fact a continuous variable? Second, the intraobserver variability and interobserver variability in the study were very low at less than 5% each, but we wonder if this will hold true for the external validity of the results. Third, noninvasive assessment of renal-allograft function is an actively pursued area of investigation in many centers, including ours. In that regard, various types of magnetic resonance imaging (MRI), including blood oxygen level–dependent MRI,2 arterial spin labeling MRI,3 and diffusion-weighted MRI,4 also seem to have shown promising results.