Eating and drinking normally before a contrast CT scan

The guideline. The ESUR 2026 handbook: "Fasting is not recommended before administration of low- or iso-osmolar non-ionic iodine-based contrast media, gadolinium-based agents or ultrasound contrast agents", explaining that the practice dates from high-osmolar agents that made many patients vomit. FDG PET is different: there, fasting is part of the test.

The trials. At a Brazilian cancer centre, 3,206 outpatients were randomised to fast for at least 4 hours or have a light meal; adverse symptoms after contrast were reported by 1.5 per cent and 0.9 per cent, not a significant difference (Barbosa 2018). In 2,091 hospital inpatients randomised to fast for at least 4 hours or eat freely, there was no aspiration pneumonitis in either group and nausea (6.6 against 7.6 per cent) and vomiting (2.6 against 3.0 per cent) did not differ significantly (Neeman 2021). In 1,103 Spanish outpatients, nausea and vomiting were less common without fasting (0.92 against 2.86 per cent) and overall acute reactions did not differ (Zitan Saidi 2024). A meta-analysis of ten studies with 308,013 patients found no aspiration pneumonia and the same pooled rate of nausea, 4.6 per cent, with and without fasting (Choi 2023).

The gap. No survey OnCo found measures how many departments still ask patients to fast; the authors of the 2024 trial write that many European patients still experience the practice. For people with cancer who are already eating poorly, or who have diabetes, hours without food before every staging scan is a burden with no benefit shown.