Duplex Doppler sonography of renal transplants: lack of sensitivity and specificity in establishing pathologic diagnosis

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Abstract
Recent reports have suggested the value of duplex Doppler sonography in the assessment of renal transplant function. Accurate diagnosis of acute rejection and its distinction from acute tubular necrosis and cyclosporine A toxicity have been claimed. We undertook a combined retrospective and prospective analysis of duplex Doppler examinations performed over a 2-year period to assess the value of such studies in evaluating renal allograft dysfunction. Seventy-seven sonographic examinations were performed on 77 renal transplants. A mean resistive index was calculated from Doppler measurements within main, segmental, and interlobar renal arteries by using the following ratio. peak systolic blood-flow velocity--minimum end-diastolic blood-flow velocity/peak systolic blood-flow velocity Forty-eight Doppler results were correlated with transplant biopsies and 29 with clinical course. Twenty-three episodes of acute allograft rejection were confirmed. When a resistive index of greater than or equal to 0.9 was used to indicate acute rejection, sonography had a sensitivity of only 9% and a specificity of 91% for this diagnosis. In one of eight cases of cyclosporine A toxicity and in three of six examples of acute tubular necrosis, the resistive index was greater than 0.9. In all six instances of chronic rejection, the resistive index was less than 0.84. None of eight patients with evidence of infection had a resistive index greater than 0.9. The resistive index range of 12 normally functioning allografts was 0.57-0.69. Correlation between the resistive index and the severity of arterial and arteriolar changes on biopsy was poor. An increased resistive index of renal transplant blood flow, as measured by duplex Doppler sonography, usually signals pathologic changes in an allograft. However, our data indicate that this test is not as sensitive or specific in identifying the cause of transplant dysfunction as has been suggested previously.