Severely elevated intrarenal arterial impedance and abnormal venous flow pattern in a normal functioning kidney graft.

Serial Doppler sonographic impedance measurements represent the most common diagnostic method for noninvasive monitoring of kidney grafts. Severely elevated arterial impedance is almost always associated with graft dysfunction. However, we describe in the present work a renal transplant recipient with optimal graft function despite permanently elevated arterial impedance (pulsatility index (PI) ranging from 2.9-3.0, and resistive index (RI) = 1.0 as well as an abnormal venous flow pattern. In contrast, the contralateral graft from the same cadaver donors transplanted into a 17-year-old female patient displayed normal range PI and RI values in conjunction with a normal serum creatinine. Known causes of arterial impedance elevation such as rejection, cyclosporine, urinary obstruction, and external graft compression were excluded. Other extrarenal causes of high impedance, such as aortic insufficiency and reduced aortic compliance, were also excluded. No evidence of impaired venous outflow at the site of the anastomosis of the main renal vein to the iliac vein was found. Those findings support the view that impedance indexes are hemodynamic rather than functional parameters.