Comparison between Doppler Ultrasound and Biopsy Findings in Patients with Suspected Kidney Transplant Rejection

Abstract

Introduction: The role of Doppler ultrasound in diagnosing kidney allograft rejections is controversial. Our goal in this study was to investigate the utility of Doppler-measured resistive index (RI) as a screening tool for kidney transplant rejection.
Methods: We retrospectively studied a random sample of 188 kidney transplanted patients who had Doppler-ultrasound examination followed within two weeks by transplant biopsy. We evaluated the specificity and sensitivity of Doppler ultrasound in diagnosing rejection at different RI thresholds, using the reported biopsy findings as the gold standard.
Results: The RI values of the study population had a mean value of 0.7 ± 0.11 (mean ± SD) and a range of 0.4-1.0. There was no significant difference in the mean RI between patients with biopsy proven rejection and patients without rejection (0.68±0.09 versus 0.71±0.12, P = 0.16). The sensitivity and specificity of Doppler-measured RI in diagnosing rejection was highly variable depending on the chosen cut-off value, ranging between 4.1-98.6% and 2.6-92.2% respectively. Acceptable specificity was only achieved at the expense of very low sensitivity. Acute tubular necrosis (ATN) and interstitial edema (IE) were associated with higher RI values than other pathological entities, while very low RI values had high specificity and low sensitivity for transplanted renal artery stenosis (TRAS).
Conclusion: Doppler-measured RI lacks accuracy in diagnosing transplanted kidney rejection, resulting in poor utility of this test as a screening tool for rejection.

Keywords: Doppler Ultrasound; Rejection; Resistive Index (RI); Transplant kidney