Objectives: To compare the performance of Doppler ultrasound (US) and US elastography with their combination in detecting delayed graft rejection.

Methods: A prospective cross-sectional study of 60 consecutive adult kidney transplant recipients was done. Patients with creatinine > 1.5 mg/dL and a minimum interval of 3 months from renal transplant surgery were recruited. All patients underwent both Doppler US and US elastography. A direct head-to-head comparison was made. A glomerular filtration rate (eGFR) < 50 was regarded as delayed graft rejection. A resistive index (RI) value ≥ 0.79 was considered abnormal.

Results: RI was more strongly correlated to age, diabetes mellitus, and hypertension with Pearson correlation coefficients of 0.414, 0.390, and 0.386, respectively, while stiffness (kPa) exhibited a stronger correlation to the time period since surgery. Using radiological findings to estimate observed eGFR showed an adjusted R² of 0.135. Doppler US alone, US elastography alone, and combined Doppler US + US elastography + clinical data, respectively, showed area under curve (AUC) values of 0.668 (95% CI = 0.535 to 0.735), 0.641 (95% CI = 0.507 to 0.761), and 0.792 (95% CI = 0.667 to 0.886) in detecting delayed graft rejection. Estimating RI using clinical and US elastography findings showed AUC of 0.811 (95% CI = 0.689 to 0.901), with sensitivity of 61.5% (95% CI = 40.6 to 79.8) and specificity of 91% (95% CI = 76.3 to 98.1).

Conclusion: Monitoring renal allografts using a combination of Doppler US and US elastography, in conjunction with clinical data, may provide additional early diagnostic and clinical advantages.