The friendship score: a novel composite arterial calcification-to-distance ratio predicts delayed graft function after living donor kidney transplantation

Dingran Li^1,2,#, Jingcheng Lyu^1,2,#, Yichen Zhu^1,2,*
1 Department of Urology, Beijing Friendship Hospital, Capital Medical University, Beijing, China
2 Institute of Urology, Beijing Municipal Health Commission, Beijing, China
* Corresponding Author: Yichen Zhu. Email: email
# Dingran Li and Jingcheng Lyu are co-first authors

Canadian Journal of Urology https://doi.org/10.32604/cju.2026.084467

Received 23 April 2026; Accepted 14 July 2026; Published online 18 August 2026

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Abstract

Objective: Although iliac artery calcification has been recognized as an important prognostic factor affecting renal transplant outcomes, its quantitative integration into a practical predictive model for Delayed Graft Function (DGF) remains lacking. This study therefore aimed to identify independent risk factors for DGF and develop a composite predictive model based on iliac artery calcification. Methods: This retrospective study included 257 patients who underwent living donor renal transplantation from January 2017 to October 2025. Clinical data, including conventional risk factors, and pre-operative CT measurements of iliac artery calcification score (Agatston score) and plaque-to-anastomosis distance, were collected. Multivariate logistic regression identified independent risk factors and informed the construction of three computational models combining calcification burden and distance. The Calcification-to-Distance Ratio A (CDR-A) model, defined as the ratio of the iliac artery calcification Agatston score to the minimum distance between the nearest calcified plaque and anastomotic site, proved to be the most effective parameter termed the “Friendship Score”. Predictive accuracy was assessed via ROC curve analysis, and clinical utility was evaluated using Decision Curve Analysis (DCA). Results: Higher BMI (p < 0.05), longer warm ischemia times (p < 0.05), and Calcification in the iliac artery planned for anastomosis (p < 0.05) were independent DGF risk factors. The CDR-A model (AUC = 0.806, 95% CI [0.666–0.946]) demonstrated superior predictive performance for DGF. DCA confirmed the meaningful clinical utility of the CDR models. The Friendship Score provides a superior composite measure of calcification risk. A score > 13.06 cm⁻¹ in Living Donor indicates high DGF risk. Conclusions: The Friendship Score, with a cut-off value of 13.06 cm^⁻¹, serves as a practical pre-transplant predictor of DGF and aids in identifying candidates who may benefit from alternative arterial anastomosis.