NPO Requirements for CT Scans

For most CT scans, patients do not need to be NPO, with the important exception of FDG-PET/CT scans which require at least 4 hours of fasting. 1

Standard CT Scans (Non-PET)

Recent high-quality evidence demonstrates that fasting is unnecessary for contrast-enhanced CT scans. A 2021 randomized controlled trial of 2,091 hospitalized patients found that withholding fasting orders prior to contrast-enhanced CT was not associated with any cases of aspiration pneumonitis in either the fasting or non-fasting groups, and rates of nausea and vomiting were statistically identical between groups (6.6% vs 7.6% for nausea, 2.6% vs 3.0% for vomiting). 2
Even when oral contrast is administered, the same study found no significant difference in adverse outcomes between fasting and non-fasting groups (nausea 6.8% vs 8.0%, vomiting 2.6% vs 3.6%). 2
In pediatric populations, administering oral contrast within 2 hours of propofol sedation for abdominal CT appears safe, with no significant differences in adverse events compared to traditional NPO timeframes. 3

Non-contrast CT scans require no special preparation and can be performed without fasting, as demonstrated in emergency department protocols for appendicitis evaluation and ureterolithiasis assessment. 4, 5
A 2023 quality assurance study during iodinated contrast shortage showed that non-contrast CT had 94% sensitivity and 100% specificity for acute abdominal complaints, with only three missed findings among 424 patients. 6

Patients without diabetes must abstain from all food, simple sugars, and beverages (except plain unflavored water) for a minimum of 4 hours prior to FDG injection. 1
Intravenous glucose solutions and parenteral nutrition must be halted at least 4 hours before FDG administration. 1
Coffee and caffeinated beverages are not recommended, even if "sugarless," as they may contain traces of simple carbohydrates and have excitant effects. 1

The primary objective of fasting is to ensure low blood glucose levels and low insulinemia, as insulin directly drives glucose uptake by non-tumor cells, which would reduce FDG accumulation in target areas and increase background uptake in normal tissues. 1

The American College of Radiology lists oral contrast as institution-specific and optional for many indications, including right lower quadrant pain evaluation. 4
Emergency department protocols have successfully eliminated routine oral contrast for appendicitis evaluation without requiring repeat scanning (0% repeat rate in one 311-patient series). 4

If using IV contrast, adequate prehydration (e.g., 1 liter of water 2 hours prior to injection) is important to minimize contrast concentration in urine and reduce risk of kidney injury, but this does not constitute an NPO requirement. 1

Do not confuse sedation requirements with CT scan requirements. If sedation is planned, American Society of Anesthesiologists guidelines recommend 2 hours of fasting for clear fluids, but this is a sedation requirement, not a CT requirement. 3
Do not apply outdated fasting protocols reflexively. The 2021 randomized trial provides Level 1 evidence that routine fasting before contrast-enhanced CT is unnecessary and does not improve safety outcomes. 2
Always verify if the scan is FDG-PET/CT versus standard CT, as only PET/CT requires fasting due to the metabolic imaging component. 1