After your CT contrast/dye injection

Although a reaction to the contrast/dye injection is extremely rare after your CT contrast/dye injection, we will ask you to wait in the department with the cannula in your arm for a minimum of 15 minutes. We keep the cannula in place in case we need to give you some medication if you have a reaction.

If a reaction does occur, this usually happens shortly after the injection. These effects are usually very mild and do not last long.

A reaction may show itself as one of the following:

  • skin rash, lumps, itchy spots or other allergic symptoms,
  • stinging pain at or near the injection site,
  • wheeziness, difficulty in breathing or tightness or pain in the chest,
  • dizziness or feeling faint,
  • swelling of your face,
  • a fever or high temperature,
  • an unexpected change in the amount of urine produced and/or its appearance,
  • abdominal discomfort,
  • nausea, vomiting and/or diarrhoea,
  • swelling or tenderness of your salivary glands in your throat, or

It is important to stay well hydrated following the contrast injection to help flush the contrast/dye out of your system. We advise drinking between 2 to 3 litres of water over the next 24 hours.


If you experience any of the symptoms listed above within 24 hours of the CT contrast injection, please contact the centre where your injection was administered on one of the numbers below.

Radiotherapy pre-treatment department

  • The Christie at Withington – 0161 446 3000
  • The Christie at Oldham – 0161 918 7700
  • The Christie at Salford Royal – 0161 918 7800
  • The Christie at Macclesfield – 0161 956 1700

If you cannot get through to the specific centre where you had your contrast injection, please contact any one of our radiotherapy centres, Monday to Friday, 8am to 6pm.

Diagnostic CT scanning (department 11)

If you are asked to stop taking metformin 48 hours post contrast injection, please organise a blood test to check your eGFR with your GP 2 to 4 days post scan. Monday to Friday, 8am to 5pm, please contact the cross-sectional radiographer on 0161 446 3884.

Proton beam therapy unit

Monday to Friday, 8am to 6pm, please contact proton beam therapy reception 0161 918 7577 or 1195.

Outside of these hours, contact your GP or the NHS 111 service, or the nearest Accident and Emergency department. If the symptoms listed above become severe or last for more than a few days, please contact your GP or nearest Accident and Emergency Department. Sometimes medical treatment is necessary.

Last updated: April 2024