Color Doppler ultrasound in renal transplant: role of resistive index versus renal cortical ratio in the evaluation of renal transplant diseases.

BACKGROUND/AIMS: Ultrasound (US) and color Doppler are not sensitive enough to detect anomalies in cortical perfusion, which is affected in most graft dysfunctions. The renal cortical ratio (RCR) is a variation in the resistive index (RI) values from the renal artery to cortical vessels, expressed in percent. The aim of this study was to compare the RI and RCR in the differentiation of normal and pathological grafts, to assess the positive predictive value of RCR and show that RCR enables earlier diagnosis than RI. METHODS: Based on clinical, biochemical and histological examinations, 494 renal allografts were divided into 3 groups (normal grafts, acute and chronic pathologies). All patients underwent US color Doppler. RI was measured and RCR calculated. Follow-up confirmed the initial division in groups. Statistical significance was calculated using the two-tailed Student's t test. The positive predictive value was calculated for each group. RESULTS: 24 h after transplant, RCR differentiated normal grafts from acute dysfunctions despite confusing biochemical values and clinical symptoms. In chronic patients, RCR variations occurred later but always before the serum creatinine level increased. CONCLUSION: RCR presented a higher positive predictive value than RI. RCR curves were already altered in the early stages of transplant pathologies. RCR calculation is easy and makes a significant contribution towards a correct early diagnosis.