Diagnostic accuracy of MRI and US for identifying acute rejection after allogeneic kidney transplantation: a systematic review and meta-analysis.

objectivesTo evaluate the diagnostic performance of multiparametric Magnetic Resonance Imaging (MRI) and Ultrasound (US) for detecting Acute Immune Rejection (AIR) after kidney transplantation through a systematic review and meta-analysis.

methodsFive electronic databases were systematically searched up to May 30, 2025. Eligible studies included kidney transplant recipients assessed with noninvasive imaging for AIR and reporting diagnostic accuracy. Two reviewers independently performed study selection, data extraction, and quality assessment using the Quality Assessment of Diagnostic Accuracy Studies-2 (QUADAS-2). Given the heterogeneity of imaging modalities, MRI and US studies were analyzed separately, and subgroup analyses and meta-regression were performed to explore sources of heterogeneity.

resultsEighteen studies (1140 cases; 494 AIR and 646 non-AIR) were included. For MRI, the pooled sensitivity, specificity, and Area Under the Curve (AUC) were 0.89, 0.91, and 0.96, respectively. For US, the pooled sensitivity, specificity, and AUC were 0.79, 0.89, and 0.90, respectively. Substantial between-study heterogeneity was observed. Meta-regression and subgroup analyses suggested that heterogeneity was associated with reference standard and imaging timing.

conclusionMRI and US demonstrate promising accuracy for detecting AIR after kidney transplantation. However, the available evidence remains limited in scale, and substantial heterogeneity exists across studies. Therefore, MRI and US should be considered adjunctive tools rather than replacements for histopathological biopsy. Further large-scale, prospective studies are required to validate their clinical utility.