Renographic indices for evaluation of changes in graft function

Radionuclide renal diagnostic studies play an important role in assessing r enal allograft function, especially in the early post-transplant period. In the past two decades various quantitative parameters have been derived fro m the radionuclide renogram to evaluate chang es in perfusion and/or functi on of the kidney allograft. In this review article we discuss the quantitat ive parameters that have been used to assess graft condition, with emphasis on the early postoperative period. These quantitative methods are divided into parameters used for assessing renal graft perfusion and parameters use d for evaluating parenchymal function. The blood flow in renal transplants can be quantified (a) by measuring the rate of activity appearance in the k idney graft, (b) by calculating the ratio of the integral activity under th e transplanted kidney and arterial curves and (c) by calculating the renal vascular transit time. In this article we review a number of parenchymal up take and excretion indices, such as the accumulation index, the graft uptak e capacity at 2 and 10 min, the excretion index and the elimination index. The literature on these parameters shows that they have some practical disa dvantages. In addition, values suffer from significant overlap when various graft pathologies coexist. A retrospective study was designed in our insti tution to evaluate the clinical usefulness of some of the frequently used p reviously published methods in which the graft function is quantitatively a ssessed in the early post-transplant period. The quantitative parameters st udied which were reasonably reproducible in our hands included: global perf usion index (GPI), cortical perfusion index (CPI), vascular transit time, a nd the parenchymal parameters uptake capacity at 2 min (UC2) and eliminatio n index (K-3/20). The patient population in this study consisted of 43 pati ents with 157 technetium-99m mercaptylacetyltriglycine renograms. The perfu sion indices GPI and CPI did not allow differentiation of the acute tubular necrosis (ATN) group from the acute rejection (AR) group; however, they we re of value in monitoring the improvement in the condition of the graft dys function in both the AR and ATN groups. As for the parenchymal parameters, both UC, and K3/20 were able to differentiate stable graft function (SGF) v ersus AR and ATN groups but were unable to separate AR from ATN dysfunction . The ability of these parenchymal parameters to detect improvement in the graft function was poor and statistically non-significant. From the literat ure data and our own findings it is concluded that radionuclide scintigraph y of renal transplants has assumed an important role, especially if perform ed serially, in monitoring graft function in the post-transplant period. Ma ny quantitative parameters have been derived from the radionuclide renogram to evaluate changes in perfusion and/or function of the kidney allograft. It appears that these quantitative numerical values are unable to different iate unequivocally between grafts with ATN and AR cases. The real value of these parameters lies in the follow-up of the dysfunction processes, which helps the clinician to determine the appropriate therapeutic regimen.