Can You Eat Before a CT Scan or an MRI? Food and Drink Before a Scan

Can you eat before a CT scan? Can you eat before an MRI? For many scans the answer is yes, but some need you to stop eating for a few hours, drink extra water, or pause a supplement. The NHS says the hospital will tell you what you need to do for CT, MRI, ultrasound and X-ray, so the instructions in your appointment letter always come first.

This guide sets out what NHS hospitals typically ask before each type of scan, and why instructions differ. If anything here differs from what your clinic tells you, follow the clinic's instructions. For general tips, see our guide on how to prepare for your scan.

Can you eat before an MRI?

For most MRI scans, the NHS does not list fasting among the usual preparations. It says the hospital will tell you if there is anything you need to do before the scan, and that you can eat and drink as normal afterwards.

Some MRI scans of the abdomen are different. West Suffolk NHS Foundation Trust, for example, asks patients having an MRCP (an MRI scan of the bile ducts) not to eat or drink for 4 hours beforehand, and to avoid chewing gum or smoking, because these can stimulate the gallbladder. It asks people with diabetes to have a light snack as required. So if you are asking whether you can eat or drink before an MRI, the answer depends on which part of the body is being scanned.

Can you eat before a CT scan?

The NHS says that before a CT scan you may be asked to follow a special diet, take certain medicines, or not eat or drink anything for several hours. It also says contrast dye can be given as a drink as well as an injection.

University Hospitals Sussex, for example, asks patients who need a contrast injection not to eat anything for 2 hours before the scan. Your appointment letter will explain whether you need to fast or have a drink beforehand. See our private CT scan page for more about CT, and our guide to CT with contrast covers contrast preparation in detail.

Can I eat before an ultrasound?

The NHS says the hospital or clinic should tell you if there is anything you need to do before an ultrasound, and that you may be asked to drink a few glasses of water, without going to the toilet, so you have a full bladder. What you are asked to do depends on the area being scanned. For example, The Princess Alexandra Hospital gives these instructions for an ultrasound of the abdomen and pelvis:

• No food for 6 hours: do not eat any food for the 6 hours before, and drink only water or clear fluids (no milk or fizzy drinks). See our guide to abdominal ultrasound.
• A full bladder: drink 1 litre of water or clear fluid 1.5 hours before the appointment, to fill your bladder. See pelvic ultrasound scans.
• Other scans: the clinic will tell you what, if anything, is needed.

So if you are wondering whether to drink water before an ultrasound, the answer depends on the scan, so drink only what the clinic asks you to. Pregnancy scans are arranged through maternity care and have their own instructions.

X-rays: usually no fasting

The NHS says you will be told before your X-ray if there is anything you need to do. Depending on the type of X-ray, you may sometimes be asked not to eat or drink for several hours, or to take a medicine the day before. The NHS says this applies only sometimes, so check your instructions.

DEXA scans: pause calcium supplements

For a DEXA bone density scan, Northern Care Alliance NHS Foundation Trust asks patients who take calcium supplements to stop taking them 24 hours before the appointment, and to wear loose clothing without metal such as zips or poppers. It also asks you to tell staff if you have had any other medical tests in the last seven days. See our DEXA scan page for more.

Medicines and diabetes

In general, keep taking your usual medicines unless you are told otherwise. The Princess Alexandra Hospital tells ultrasound patients to take regular medication as usual unless instructed otherwise.

If you have diabetes, tell the clinic in advance. The Princess Alexandra Hospital gives patients with diabetes early appointments and specific instructions about their medication, and asks them to bring their tablets or insulin if they have been told not to take them. For CT with contrast, University Hospitals Sussex says diabetes medicines such as metformin may need to be stopped. Do not stop any medicine unless the clinic tells you to.

Fasting before a scan: quick summary

• MRI: the NHS does not list fasting for most MRI scans, but some abdominal scans, such as MRCP, need a few hours without food or drink.
• CT: you may need to fast for a few hours, for example before a contrast injection.
• Abdominal ultrasound: you may be asked not to eat for around 6 hours.
• Pelvic ultrasound: you may be asked to drink water beforehand so your bladder is full.
• X-ray: only some types need fasting; you will be told beforehand.
• DEXA: you may be asked to pause calcium supplements for 24 hours.

CT, X-ray and DEXA use ionising radiation, so under IR(ME)R 2017 each exposure needs a referrer and must be justified; many private clinics arrange this through their own doctor. For MRI and ultrasound, many clinics accept self-referral after their own safety screening, but each clinic sets its own policy.

When you compare clinics near you and send an enquiry through FindScan, the clinic you choose will give you its own preparation instructions. FindScan shows each clinic's own listed price, and the clinic will tell you how long its report takes.