Opportunistic CT-based screening is the practice of exploiting incidental imaging data for prevention, risk profiling, or presymptomatic detection of relevant disease unrelated to the purpose for which the imaging test was performed1. We recently demonstrated the feasibility of measuring GFR based on iomeprol clearance assessed by CT urography in living kidney donor candidates, using a value-added opportunistic imaging strategy2. This method could potentially be of interest to patients with kidney or urothelial cancer, for whom the choice or dose of chemotherapy may depend on the GFR value3,4.