Hopefully this can clarify a few misconceptions and address some concerns in this discussion, quoted from HERE
Some people have allergies to IV contrast and may need to take medications before their test in order to safely receive this substance.
Contrast can be given several ways, and depends on the type of CT being performed.
It may be delivered through a vein (IV) in your hand or forearm.
It may be given through the rectum using an enema.
You might drink the contrast before your scan. When you actually drink the contrast depends on the type of exam being done. The contrast liquid may taste chalky, although some are flavored to make it taste a little better. The contrast eventually passes out of your body through your stools.
If contrast is used, you may also be asked not to eat or drink anything for 4-6 hours before the test.
I've had oral contrast + IV contrast CTs, IV contrast only CTs and non-contrast CTs.
IV contrast is used for abdominal and thoracic CTs.
Oral contrast is used for abdominal CTs ( unless evaluation of the thoracic esophagus is indicated. )
Radiologists like contrast ..... BUTT some patients cannot handle contrast so even if it is a thoracic CT ..... the CT can still be done WITHOUT contrast.
The blood test required prior to a CT scan should be for renal function
(BUN-creatinine-eGFR), as the contrast can be hard on the kidneys and some patients are better off without it. It has nothing to do with CEA levels.
Sometimes, patients will be offered the use of acetylcysteine as a medication to limit or prevent renal problems from the IV contrast. Depending upon your own blood results, it would be best to talk to your Onc or GP if it is safe for you ... radiologists, as I said just want the contrast to be used to get the most consistent imaging.
Yes, battled Radiologists.
Yes, have had a few CTs without any contrast.
Fasting is generally good advice prior to imaging, for a lot of reasons.