The uptake of 18F-FDG by renal allograft in kidney transplant recipients is not influenced by renal function

Objectives 18F-Fluorodeoxyglucose (18F-FDG) positron-emission tomography coupled with computed tomography (PET/CT) imaging has been recently proposed as a non-invasive tool for the diagnosis of renal allograft acute rejection (AR) in kidney transplant recipients (KTR). Still, the influence of kidney function on the renal graft uptake of 18F-FDG remains debated.

Methods We retrospectively identified all KTR who underwent at least one 18F-FDG PET/CT between January 2010 and December 2015. KTR with documented pyelonephritis or AR, as well as patients under chronic hemodialysis, were excluded. Medical, biological and technical parameters were extracted from a prospective database. Estimated glomerular filtration rate (eGFR) was assessed using chronic kidney disease (CKD)-EPI equation (stage 1 蠅 90 ml/min, stage 2 60-89 ml/min, stage 3a 45-59 ml/min, stage 3b 30-44 ml/min, stage 4 15-29 ml/min, and stage 5 < 15 ml/min). Mean standardized uptake values (SUVmean) of renal graft cortex and aorta were measured in 4 and 1 volumes of interest, respectively. Spearman's rank correlation coefficient (ρ) and analysis of variance (ANOVA) were performed.

Results Eighty-two KTR aged of 58 ± 13 underwent 18F-FDG PET/CT for tumor staging (n=46), suspected infection (n=11) or fever of unknown origin (n=25). Male-to-female ratio was 1.4. Mean eGFR was 50 ± 19 ml/min/1.73m² [range: 20.7; 94.4], including CKD stage 1 (n=3), stage 2 (n=21), stage 3a (n=20), stage 3b (n=29) and stage 4 (n=9). PET/CT imaging was performed within 67 ± 15 min following injection of 3.7 ± 0.6 MBq/kg of 18F-FDG. Mean glycemia at the time of injection was 113 ± 34 mg/dl. Mean kidney and aorta SUVmean were 1.8 ± 0.2 and 1.7 ± 0.3, respectively. No significant correlation was observed between eGFR and kidney SUVmean (ρ, 0.119; p, 0.28) or aorta SUVmean (ρ, -0.144; p, 0.20) considering the whole cohort. ANOVA showed no difference of kidney (p, 0.62) and aorta (p, 0.85) SUVmean between CKD groups. Mean coefficient of variation of kidney and aorta (on the basis of SUVmean of >3 consecutive 18F-FDG PET/CT in 15 patients with no significant change of eGFR) reached 13.1% and 12.2%, respectively.

Conclusions Our data suggest that the uptake of 18F-FDG by renal allograft within an hour post injection is not significantly impacted by CKD.