Fludeoxyglucose F 18 Positron Emission Tomography/Computed Tomography: A Novel Diagnostic Tool for Immune Checkpoint Inhibitor-Associated AKI

Background: No clinical features reliably differentiate immune checkpoint inhibitor-associated AKI (ICI-AKI) from other AKI etiologies. We examined the role of F18-FDG PET-CT in diagnosing ICI-AKI. Methods: We used data from a multicenter international cohort study of 429 patients with ICI-AKI, along with data from 2 control groups: patients with acute tubular injury from non-ICI nephrotoxic chemotherapies or from the cancer itself, and patients treated with ICI therapy who did not have AKI. Patients were required to have PET-CT scans at baseline and within 14 days of AKI onset (or, for the second control group, a follow-up PET scan between 90-365 days following ICI initiation). Nuclear radiologists reviewed the PET-CTs at baseline and follow-up and recorded the mean radiotracer standardized uptake value (SUVmean) in the renal cortices. We then calculated the average percent change in SUVmean from baseline to follow-up for each patient. A receiver operating characteristic curve was generated to evaluate the accuracy of percent change in SUVmean for diagnosing ICI-AKI. Results: 53 patients were included (9 with ICI-AKI, 24 with AKI from other causes, and 20 on ICIs but without AKI). Representative images from baseline and follow-up PET-CTs are shown in Figure 1A. The median percent change in SUVmean increased by 57.4% (IQR, 40.3-119.8) from baseline to follow-up among patients with ICI-AKI, but changed minimally among patients in the two control groups (P<0.001; Figure 1B). The AUC for the differentiation of ICI-AKI from the two control groups based on percent change in SUVmean was 0.97 (95% CI, 0.93-1.00) (Figure 1C). Conclusion: F18-FDG PET-CT may be a useful test for diagnosing ICI-AKI, particularly for patients who cannot be safely biopsied due to a contraindication.