Doppler ultrasound for the evaluation of chronic renal allograft dysfunction

Chronic renal allograft dysfunction (CRAD) is a common cause of late graft failure after kidney transplantation. Puncture biopsy is the "gold standard" for the diagnosis and assessment of CRAD, but can easily lead to various complications. Thus, this study sought to identify Doppler ultrasound parameters that can accurately assess CRAD.

Kidney transplant recipients who underwent ultrasound Doppler examination between January 2011 and December 2021 at our hospital were included in the study. The CRAD group comprised patients who underwent pathology puncture within 7 days of Doppler ultrasonography and were diagnosed with chronic pathological changes by two specialized pathologists. The patients in the GRAD group were further subdivided into mild (group I) and moderate-to-severe (group II) groups based on the degree of pathological changes. Data on sex, age, body mass index (BMI), blood pressure, the estimated glomerular filtration rate (eGFR), serum creatinine (SCr), and cystatin-c (Cys-C) from three days before and after each patient's ultrasound examination were collected from the hospital's electronic medical record system. The Doppler ultrasound blood flow parameters of the transplanted kidneys were obtained using an ultrasound imaging system, and two specialized sonographers assessed the quality of the images, and images with satisfactory quality were deemed valid. Spearman rank correlation was used to analyze the relationships between the parameters. A logistic regression analysis was conducted to identify the independent significant variables. Prediction models were assessed by receiver operating characteristic (ROC) curves.

A total of 188 transplanted kidney recipients were included in this study. The CRAD group comprised 92 patients (group I comprised 45 patients and group II comprised 47 patients), aged 18-68 years, of whom, 75 were male and 17 were female. The control group comprised 96 patients, aged 19-63 years, of whom, 75 were male and 21 were female. With the exception of the arcuate artery, moderate negative correlations were observed between the end-diastolic velocity (EDV) of all the arteries and Cys-C (r_s =-0.39, P<0.05), and with the exception of the arcuate artery, moderate positive correlations were observed between the resistance index (RI) of all the arteries and Cys-C (r_s =0.38, P<0.05). The EDV of the segmental artery and Cys-C were identified as independent diagnostic factors for CRAD (P<0.05). The area under the curve (AUC) of the combined diagnostic model for the Cys-C, RI of the renal artery, and EDV of the segmental artery was 0.921, with a sensitivity of 87.0% and a specificity of 83.3%. Further, the EDV of the segmental artery and kidney length were independent diagnostic factors for mild to moderate-to-severe CRAD. The AUC of the EDV of the segmental artery and kidney length was 0.726, with a sensitivity of 87.2% and a specificity of 55.6%.

Among the Doppler ultrasound parameters, the RI of the renal artery and the EDV of the segmental artery were the most useful in the diagnosis of CRAD. Further, the combination of the EDV of the segmental artery and kidney length showed significant potential in assessing pathological changes in CRAD.