Preparing for a CT scan depends on which part of your body is being scanned and whether the scan requires contrast dye. Some CT scans need no preparation at all, while others require fasting, drinking a special liquid, or adjusting medications. Here’s what to expect so you can show up ready.
Not Every CT Scan Requires Prep
Many common CT scans need zero fasting, no lab work, and no contrast dye. These include scans of the spine (cervical, thoracic, or lumbar), lungs, sinuses, facial bones, skull, and any bone-focused scan of the arms, legs, feet, shoulders, or pelvis. If your scan falls into one of these categories, you can eat and drink normally beforehand and simply show up at your appointment.
The scans that do require preparation are typically ones that use contrast dye to make soft tissues, blood vessels, or organs show up more clearly. If your imaging center gave you specific instructions, follow those. They override any general advice.
Fasting Rules by Scan Type
Fasting prevents nausea from contrast dye and keeps your digestive tract from interfering with the images. The required fasting window varies:
- Abdomen or pelvis (soft tissue): No food for 6 hours before the exam. This applies when the scan is looking at organs like the stomach, liver, kidneys, pancreas, or bowels.
- Chest (for blood clots), neck soft tissues, kidneys/ureters/bladder, or carotid arteries: No food for 4 hours before the exam.
Clear liquids like water are generally fine during the fasting period unless your facility says otherwise. In fact, staying well hydrated before a contrast scan is a good idea, since your kidneys will need to flush out the dye afterward.
If You Need to Drink Oral Contrast
Some abdominal and pelvic CT scans require you to drink an oral contrast liquid before the scan. This coats the inside of your digestive tract so it shows up distinctly on the images. Outpatients typically start drinking it about 2 hours before the scan, while hospitalized patients begin 3 hours ahead. Your imaging center will provide the liquid and tell you when to start. It usually has a mildly chalky or slightly sweet taste depending on the type.
What to Wear and What to Remove
Wear comfortable, loose-fitting clothes with no metal. Zippers, snaps, metal buttons, and underwire bras can all create bright streaks on the images called artifacts. Many facilities will give you a gown, but wearing metal-free clothing can speed things along.
You’ll be asked to remove jewelry, watches, eyeglasses, hearing aids, belts with metal buckles, and hair clips or pins. Metal dental appliances may also need to come out. Leave valuables at home or in your car if possible.
One detail people often miss: some makeup, deodorants, and antiperspirants contain metal particles (especially aluminum) that can interfere with imaging. If the scan covers your head, neck, or chest, skip these products on the day of your appointment.
Medications to Discuss Beforehand
Most medications can be taken normally before a CT scan, but there’s one important exception. If you take metformin for diabetes and your scan involves contrast dye, your doctor may ask you to pause it. The concern is that contrast can temporarily stress the kidneys, and metformin combined with reduced kidney function raises the risk of a rare but serious condition called lactic acidosis.
The most current guidelines from the American College of Radiology say that if your kidney function is healthy (measured by a blood test called eGFR, with a result of 30 or above) and you’re receiving standard IV contrast, there’s no need to stop metformin. But if you have chronic kidney disease, acute kidney injury, or are undergoing certain arterial catheter procedures, the protocol is to stop metformin before or at the time of the scan, wait 48 hours, and only restart it after a blood test confirms your kidneys are working normally.
Your imaging center will likely ask about your medications and may run a quick blood test to check kidney function before giving contrast. Bring a list of your current medications to make this easier.
If You Have a Contrast Allergy
If you’ve had a reaction to contrast dye in the past, tell your doctor well before your appointment. You’ll likely need a premedication regimen that starts 13 hours before the scan. The standard protocol involves a steroid taken by mouth at 13 hours, 7 hours, and 1 hour before the procedure, plus an antihistamine 1 hour before. This significantly reduces the chance of another allergic reaction. Because the prep starts the night before, you need advance notice to get the prescriptions filled and take them on time.
What the Scan Feels Like
The scan itself is fast. With modern machines, the actual imaging takes only a few minutes, though the entire visit, including check-in, positioning, and any contrast preparation, usually runs about 30 minutes total.
You’ll lie on a narrow table that slides into a large, ring-shaped machine. It’s open on both ends, so it feels less enclosed than an MRI. You’ll need to hold still and may be asked to hold your breath briefly for chest or abdominal scans. The machine makes soft whirring or clicking sounds as it rotates around you.
If you receive IV contrast, a technologist will insert a small needle into a vein in your arm. When the dye is injected, you’ll likely feel a warm sensation spreading through your body, sometimes described as a flush that briefly makes you feel like you’ve wet yourself (you haven’t). Some people notice a metallic taste in their mouth. Both sensations fade within a minute or two and are completely normal.
After the Scan
If your scan didn’t involve contrast, there’s nothing special to do afterward. You can eat, drink, and go about your day immediately.
If you did receive IV contrast, drinking plenty of water for the rest of the day helps your kidneys clear the dye. There’s no magic number, but aim to drink more than you normally would over the next 12 to 24 hours. Oral fluids are helpful, though people with existing kidney concerns may receive IV fluids at the facility as a precaution.
Breastfeeding After a Contrast Scan
If you’re breastfeeding, you do not need to pump and dump after receiving iodinated IV contrast. Both the American College of Radiology and the Academy of Breastfeeding Medicine confirm it’s safe to continue nursing. Only a tiny amount of contrast passes into breast milk, and it isn’t harmful to the baby. The taste of the milk may change slightly for a short time, but that’s the only effect.
Quick Prep Checklist
- Confirm with your facility: Ask whether your specific scan requires fasting, contrast, or lab work.
- Follow fasting instructions: 6 hours for abdominal soft-tissue scans, 4 hours for chest, neck, kidney, or carotid scans.
- Stay hydrated: Drink water unless told otherwise.
- Wear metal-free clothing: No zippers, snaps, or underwire.
- Skip makeup and deodorant: Especially near the scan area.
- Bring your medication list: Flag metformin or any previous contrast reactions.
- Remove jewelry and accessories: Including hair clips, watches, and hearing aids.
- Plan for about 30 minutes: The imaging is quick, but allow time for the full process.