A multicenter prospective validation cohort does not confirm the diagnostic yield of FDG PET/CT imaging in kidney allograft subclinical rejection

BackgroundSubclinical kidney allograft acute rejection (SCR) corresponds to "the unexpected histological evidence of acute rejection in a stable patient". The diagnosis of SCR relies on surveillance biopsy. Positron emission tomography (PET/CT) after injection of F18-fluorodeoxyglucose ([18F]FDG) has been proposed as a non-invasive screening approach. In the present multicenter prospective study, we assess the diagnostic yield [18F]FDGPET/CT to rule out SCR in stable KTR at 3 months post KTx. MethodsFrom 01/2021 to 03/2025, we prospectively combined surveillance biopsy and [18F]FDGPET/CT at [~]3 months post transplantation in adult kidney transplant recipients from 4 independent imaging centers. The mean standardized uptake value (mSUV) was measured in kidney cortex and referenced as a ratio to psoas muscle mSUV (mSUVR). ResultsOur multicentric 185-patient cohort was categorized upon Banff-2022: normal (n=158); borderline (n=18); SCR (n=9, including 6 T-cell-mediated rejection and 3 microvascular inflammation). No significant correlation was observed between the mSUVR and ti score (R=0.032, p-value=0.67). The mSUVR reached 2.33 [1.97-2.93], 2.71 [2.50-3.33] and 2.42 [2.27-3.14] in normal, borderline and SCR groups, respectively. In multivariate models stratified by center, the risk of non-normal histology (n=27, including borderline and SCR) increased with donor age (OR=1.05 [1.01-1.1], p=0.02) but not with the mSUVR (OR=4.11 [0.91-18.48], p=0.07). The risk of biopsy-proven SCR (n=9) was not significantly associated with mSUVR. ConclusionsThe mSUVR of [18F]FDG PET/CT does not reliably rule out SCR on surveillance biopsy.