[Duplex Doppler study of the transplanted kidney].

The authors examined 34 renal transplant recipients with Duplex US, i.e. real-time sonography associated with pulsed Doppler, thus obtaining morphological and structural data about transplanted kidneys as well as hemodynamic information. Special emphasis was put on intrarenal vascular impedance and the relative resistive index, first mentioned by Rifkin in 1987. US diagnosis was compared with the results obtained at both biopsy and clinical follow-up. Only long-term renal transplants were considered; the patients were examined for a rise in serum creatinine level or for the onset of other signs/symptoms related to renal allografts. Our results confirm the utility of pulsed Doppler US in the diagnosis of renal transplant rejection, and allow reference values to be established for the resistive index. In agreement with literature data and assuming 0.9 as a resistive index value, Duplex-Doppler US specificity in diagnosing acute rejection was 100%, and sensitivity was 50%. However, the authors believed it more useful to assume 0.8 as a reference value for the resistive index, for it allows more renal transplant rejection episodes to be diagnosed, both acute and chronic, with an acceptable combination of specificity, sensitivity and predictive value. While the differential diagnosis of acute and chronic rejection is hardly ever possible with Duplex US alone, the combined use of Duplex US and real-time US makes it nearly always possible. As far as intrarenal impedance is concerned, our results seem to disagree with the scattered literature data on the subject, and to point towards its possible significant (though not extreme) increase also in case of chronic rejection.