Image-derived index - as a paramether for the semi-quantitative assessment of global tubular renal function

Introduction. Radionuclide methods are used in the evaluation of different aspects of renal function. The aim of this study was to define and implement an index derived from scintigraphic image and to compare it with ortho-iodohippurate clearance values, an indicator of effective renal plasma flow. Material and Methods. A retrospective analysis included 67 adult patients, who underwent static renal scintigraphy and ortho-iodohippurate clearance. We computed the background-to-renal index that represents the ratio of average values of counts per pixel in the background regions and in the regions of kidneys. Patients were divided into three groups according to the values of measured effective renal plasma flow: group 1 - patients with mild renal dysfunction (reduction of effective renal plasma flow ? 20%, 17 patients), group 2 - moderate dysfunction (reduction of effective renal plasma flow 20-50%, 25), and group 3 - severe dysfunction (reduction of effective renal plasma flow 50-70%, 25 patients). Results. Subjects with mild effective renal plasma flow reduction had significantly lower background-to-renal index values compared to those with moderate and severe reduction [(0.105 ? 0.05) vs. (0.134 ? 0.056) vs. (0.275 ? 0.154), p < 0,001]. A significant linear correlation was found between background-to-renal index and effective renal plasma flow (r = 0.60, p < 0.0001). Sensitivity and specificity of the calculated cut-off value of 0.1335, for the differentiation between the patients with renal reduction higher and lower than 20%, were 62% and 100%, respectively (area under curve 0.85). Conclusion. The background-to-renal index is a simple method for semiquantitative estimation of global tubular renal function that can be a useful tool when determining patients for further in vitro assessment of global renal function.