If your scan uses contrast, the main preparation is telling the team a few things: any allergies, asthma, a previous contrast reaction, kidney problems, diabetes or metformin, and whether you could be pregnant. For an injected-contrast CT you'll usually fast for a few hours (water is generally fine), and you may need a recent kidney blood test. Drink plenty of fluids afterwards to help clear the dye.
Key takeaways
- Tell the team about allergies, asthma or any previous contrast reaction.
- Declare kidney problems, diabetes or metformin — you may need a kidney blood test.
- Mention if you could be pregnant or are breastfeeding.
- For injected-contrast CT you'll usually fast a few hours; water is generally allowed.
If your scan uses contrast dye, a little preparation keeps it safe and smooth. The most important part is answering the screening questions honestly.[2]
What you’ll be asked
Before contrast, the clinic will ask whether you:[1]
- have ever had contrast before, and whether you reacted to it (and what happened);
- have asthma;
- have allergies to foods, medications, dyes or anything else;
- have diabetes or take metformin;
- have reduced kidney function or kidney disease;
- have thyroid disease or heart disease;
- could be pregnant, or are breastfeeding.
If you’re unsure of any answer, your referring doctor can usually help. These questions let the team decide whether contrast is safe for you, or whether a different test is better.[1]
Fasting and the kidney check
For an injected-contrast CT, you’ll usually be asked to fast for about 2–4 hours, though you can generally still drink water — staying hydrated actually helps.[2] If your scan uses a barium or iodine drink for the bowel, you may be given it to take at set times before or on arrival. If you have kidney disease, diabetes or take metformin, bring your most recent kidney-function blood test; the clinic may want it checked closer to the appointment.[2]
On the day and after
A small cannula is placed in a vein for the injection. When contrast goes in, a brief warm flush and metallic taste are normal. Afterwards, unless you’ve been sedated, there’s no recovery period — you can return to normal activities and eating.[1] Drink plenty of fluids to help your body clear the contrast through your urine.
Frequently asked questions
Do I need to fast for a contrast scan?
For an injected-contrast CT, usually yes — a few hours, with water generally allowed. Follow your clinic’s specific instructions.[2]
What’s the most important thing to tell the clinic?
Any previous reaction to contrast, asthma or allergies, and any kidney problems — these most affect how the team manages your contrast safely.[1]
Can I drive and eat normally afterwards?
Yes, in almost all cases — unless you were sedated for the procedure, there’s no recovery period after contrast.[1]
Sources
- RadiologyInfo.org (RSNA & ACR) — Contrast Materials — www.radiologyinfo.org/en/info/safety-contrast
- RANZCR / InsideRadiology — Iodine-containing contrast medium (ICCM) — www.insideradiology.com.au/iodine-containing-contrast-medium/
