[(68) Ga]Ga-FAPI uptake correlates with the state of chronic kidney disease

Purpose Kidney fibrosis leads to a progressive reduction in kidney function ultimately resulting in kidney failure. Diagnostic tools to detect kidney fibrosis are all invasive in nature requiring kidney biopsies with subsequent histological validation. In this retrospective study, the diagnostic value of three different radiotracers for the noninvasive prediction of kidney fibrosis was analyzed, taking into account the glomerular filtration rate (GFR) and the intra-renal parenchymal radiotracer uptake. Methods In 81 patients receiving either one of the following molecular imaging probes, [(68) Ga]Ga-FAPI, [(68) Ga]Ga-PSMA, or [(68) Ga]Ga-DOTATOC, kidney function parameters were correlated with SUVmax and SUVmean of the renal parenchyma and background activity measured in lung parenchyma, myocardium, gluteal muscle, and the abdominal aorta. Patients were clustered according to their grade of chronic kidney disease (CKD), and a regression analysis and one-way ANOVA were conducted in this retrospective analysis. Results We found a negative correlation between GFR and [(68) Ga]Ga-FAPI uptake for both SUVmax and SUVmean values, whereas background activity showed no correlation with GFR. [(68) Ga]Ga-DOTATOC and [(68) Ga]Ga-PSMA did not correlate between CKD stage and intra-renal parenchymal radiotracer uptake. Only [(68) Ga]Ga-PSMA background activity exhibited a positive correlation with GFR suggesting an unspecific binding/retention potentially due to longer circulation times. Conclusion There is a significant negative correlation between renal parenchymal [(68) Ga]Ga-FAPI uptake and GFR, which was not the case for [(68) Ga]Ga-DOTATOC and [(68) Ga]Ga-PSMA. This correlation suggests a specific binding of FAPI rather than a potential unspecific retention in the renal parenchyma, underlining the potential value of [(68) Ga]Ga-FAPI for the noninvasive quantitative evaluation of kidney fibrosis.