Ultrasonographic determination of resistive index and graft size for evaluating clinical feline renal allografts

Ultrasonographic examination is a commonly employed technique for postoperative renal allograft evaluation after transplantation. Allograft size and resistive index (RI) are two objective ultrasonographic measures that may help establish a diagnosis and direct postoperative management for grafts with suboptimal function but their diagnostic efficacy has not been evaluated in clinical veterinary patients. Results of 69 feline renal transplant ultrasonographic examinations and RI determinations were studied. Based on clinical parameters at the time of the ultrasonographic examination, patients were grouped into six clinical/functional categories including evaluations of clinically normal grafts, delayed graft function, ureteral obstruction, uroabdomen, graft thrombosis, and rejection. RI, graft size (length, cross-sectional area, and volume), cyclosporine A whole blood trough concentration, Doppler blood pressure, creatinine concentration, and days from transplantation were compared between these categories and associations with each other were examined. RI was of little value in differentiating among the clinical categories with the exception of graft thrombosis. Graft volume and time from transplantation were significantly greater in grafts with signs of rejection and ureteral obstruction compared to clinically normal ultrasound examinations. Graft volume, cross-sectional area and length were generally associated. Cyclosporine A blood concentrations was associated with RI in both the pooled data and in the delayed graft function category. These results indicate RI should be used only as part of a larger clinical picture and in light of other factors including cyclosporine A concentration and the timing of the study relative to the implantation surgery for the diagnosis of postoperative transplantation complications. Graft volume may provide a more sensitive, albeit, nonspecific, indicator of allograft dysfunction.