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Having a CT (CAT) Scan? Know what to expect!

Updated on August 25, 2011
Omnipaque is one type of X-Ray Dye a facility will administer to a patient
Omnipaque is one type of X-Ray Dye a facility will administer to a patient

So - You're scheduled for a CT Scan?

A lot of people have a lot of questions before they go in for their scheduled CT exam. Keep reading to know what to expect. The first thing you should know is that a CT Scan IS NOT AN MRI. You can have metal on your body, but anything that is removable in the area being scanned should be removed. If you are unsure if you even need the test be sure to ask questions!

X-Ray Dye

Also, a lot of people have questions about the CT Contrast, or "Dye." The dye is a solution that the technologist will inject to highlight blood vessels, and anything that has blood flowing through it. It's extremely important and helps to diagnose a ton of problems. These days, not too many people have allergic reactions to the dye as they did in the past. It's normally a newer contrast (our hospital uses Isovue-300 or Isovue-370) and most reactions to it are normal. However, be sure you tell your doctor if you have had any type of serious or minor reaction to this dye, as you may need pre-medication before the injection. Also tell your doctor and the technologist performing the exam if you have a medical history (yourself, not your family) of a brain bleed, diabetes, kidney failure, sickle cell anemia (if you have the disease, not a carrier), multiple myeloma (bone cancer), pheochromocytoma (an adrenal gland disorder), or thyroid disorders.

Normal IV Dye reactions are:

  • Headache
  • Warmth (all over, you'll probably feel very weird)
  • Nausea or Vomiting
  • Joint or muscle pain
  • Numbness, tingling sensation
  • Chills
  • Ringing in your ears
  • A taste (described as sucking on a penny or swallowing ink)
  • A urinating sensation (it feels very warm down there, so you feel as though you wet yourself)

Seek emergent treatment if you have the following symptoms within 24 hours of contrast injection:

  • Urinary symptoms (not going, or going less)
  • Severe headache with nausea and vomiting lasting several days
  • Seizures
  • Syncope (light-headedness, passing out)
  • Difficulty breathing
  • A developing rash or hives
  • Swelling anywhere

You may have had the dye before, they use it in other X-Ray procedures such as an IVP (so some call it IVP dye) or a heart cath. And remember, it's injected. So you have to get an IV put in. For more information on how the dye works, visit my article on X-Ray Dye. I have some pictures there that will hopefully help you understand it better.


If you are a diabetic, make sure that you let the technologist know. Certain diabetes medication, such as metformin, glucophage, and more, can interfere with the dye and cause kidney failure.

Why the Long Wait?

If you are getting your exam done as an outpatient in the hospital, there are multiple reasons why you must wait. If you are over a certain age (60 is the age at the hospital I work at), a creatinine test must be drawn. It's a kidney function test, and the results must be retrieved before the administration of the contrast dye. Other reasons for the creatinine test to be drawn are because of diabetes and a history of kidney problems. Some places can draw up the labs and have the results in 5 minutes. Others need to run it through their lab systems and it can take about an hour. If you know you are going to have the contrast, be sure to get the labs drawn at the doctors office where the procedure was scheduled to save yourself the time.

Another test that will be drawn is a pregnancy test if you are a female who is of age to have a child. Some places won't take your word for it that you are not pregnant. Just take the test, it takes 5 minutes, and is relatively easy.

Another reason for a wait could be because you had to drink barium.

Readi-cat is a type of barium that a facility will use. There are multiple flavors, but all are disgusting.
Readi-cat is a type of barium that a facility will use. There are multiple flavors, but all are disgusting.


If you are having a CT Scan of your abdomen and pelvis, more than likely you were asked to drink barium. It's gross, and everybody hates it. It's a necessary evil for the test, though. Barium acts in a way similar to the dye, except it's for the digestive system.

In my experience I've never ever ever ever had a patient who was allergic to the barium, and never heard of it. More than likely if a patient says they are, it's because it's icky and they don't want it. When you drink the barium, it coats your digestive system to highlight it, and will show off any abnormalities as well as highlight areas that could not be seen without it, such as your appendix. Normally, you have to wait an hour to an hour and a half after drinking it down before you can have your test.

Here's a tip on how to save yourself some time. Before you go to the facility where you are having your test done, ask either your doctor's office or the facility doing the scan for a bottle of the barium. Ask them "How long before my exam should I drink this?" and they will tell you. That way, you can drink it at home and not have to wait as long.

Rectal Contrast

Yes. If you are having a CT of the abdomen and pelvis, more than likely you will receive an enema of contrast that you have to hold in during the exam. It's similar to the barium, but not as thick, and you don't have to hold very much. You can refuse it, but it's not recommended as you will have a suboptimal exam, and something could be overlooked. There is a way around it though!

Drink 2 bottles! As stated before, ask the facility for a bottle of barium to take home. Tell them that you don't want them enema and you don't want a suboptimal exam, so when should you drink this to avoid the enema? Most places would be happy to do this, as they prefer not to actually give the enema either. Some facilities require 3 bottles, but normally the magic number is 2.

OK, so you've had the exam, now what?

You're done! Be sure to drink a ton of water so you don't dehydrate yourself after the dye is injected. Normally it takes about 2-3 days for your physician to get the results. The facility doing the exam can't give you the results but they can make copies via a CD or films to give to your doctor.


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