Background: Renal transplant is the gold standard therapy for irreversible chronic kidney disease. However, frequently the functional recovery of transplanted kidneys is deferred, configuring the clinical diagnosis of Delayed Graft Function (DGF), involving 25% of patients undergoing renal transplant and requiring at least one dialysis treatment in the first post-transplantation week. The purpose of our study is to validate the use of ultrasounds for the prediction of the outcome of the graft, with the aim of setting a new predictive model for grafts outcome based on Ultrasound examination.

Methods: Our study is based on two objective endpoints, both addressed on the use of ultrasounds:

• the first endpoint was pursued through a retrospective study, involving patients who underwent kidney transplant from 2013 to 2021, subjected to Color-Doppler Ultrasounds (CDU) in their 1st, 4th day after surgery and the day of clinical dimissions;
• the second endpoint was pursued through a prospective study, involving patients who underwent Contrast-Enhanced Ultrasounds (CEUS) in their 7th day after surgery.

The study was performed with Philips EPIQ 7 ultrasound scope (Philips Healthcare, Andover, MA) and SonoVue (Bracco Company, Milan, Italy) as contrast medium. For CDU the variables considered were upper and lower Resistive Indexes (RRI) and their average. Over CEUS, the Ultrasound Dynamic evaluation was performed for 1 minute. A 10mm side square region of interest (ROI) was defined on the superior polar renal cortex. QLAB Software was used to obtain quantitative analysis of renal perfusion including: 

• the slope rate of ascending curve (A), 
• the time to peak (TTP), 
• the derived peak intensity (DPI),
• the area under the curve (AUC).

Results: Our retrospective study involved 381 patients (391 grafts of which 71 DGF and 10 PNF); the univariate analysis of the results revealed that there was a statistically significant difference between upper and lower RRI and their average in patients with DGF and patients with Early Graft Function (EGF) p Value 0.0001. No correlation between RRIs and PNF was found. Our prospective study included 25 patients; 7 of them developed a DGF. The results revealed that TTP in patients with DGF seems to be reached later than in patients with EGF. AUC was lower in the DGF group. No correlation between A and DPI and functional recovery of the graft was found. Statistical Analysis of these values, althought, isn’t available yet.

Conclusions: The well-known usefulness of the color-doppler ultrasound study in the transplanted kidney is confirmed, adding to its characteristics the possibility of use as a tool to predict grafts outcome. Further studies are needed to determine CEUS capability in the prediction of grafts functional recovery and to obtain a Perfusion Index, which will be the milestone of a new predictive model based on visual and numerical feedback.