Do I need to be worried about having an allergic reaction to the iodine dye used for my CT scan? Does the dye cause any permanent damage?

Although most people have no problems with iodine contrast (or dye) which is injected intravenously (IV), there are two possible undesired complications.

One possible adverse effect is to have an allergic reaction. The reaction can range from mild (itching, rash, hives) to severe (difficulty breathing or sudden shock, which in rare instances can lead to death). It is important to tell your doctor, the person who schedules your CT scan, and/or the CT technologist if you have had a previous allergic reaction to IV contrast or if you have a history of asthma requiring the use of inhalers. In some such instances, steroid medication may be prescribed prior to the CT scan to minimize your risk of developing an allergic reaction. In the past, having an allergy to shellfish (which contains iodine) was considered a risk factor for developing an allergic reaction to IV contrast, but this is no longer considered significant.

The other possible side effect of IV contrast is damage to the kidneys, usually temporary but occasionally permanent. This is only a concern if you have poor kidney function, are dehydrated, or are diabetic. If you are taking a medicine called metformin (Glucophage) to help control your diabetes, and your kidney function labs are abnormal, you are at risk of developing a condition called lactic acidosis caused by kidney failure. For these reasons, it is important to let your doctor, the person who schedules your CT scan, and/or the CT technologist know if you have diabetes or if you are taking Glucophage. Often, your doctor will order blood tests to make sure that your kidney is functioning properly prior to the CT scan. If you are taking Glucophage, you will be asked to stop for a short period around the time of your CT scan, and can only resume taking it after your doctor has determined it is safe to do so. It is also a good idea for anyone having a study with IV contrast to drink enough fluid around the time of the CT scan to minimize dehydration, which can increase the potential for kidney damage.

I had a CT scan two days ago. I drank 3 glasses of diluted iodine prior to the test. Since yesterday, I have had diarrhea. Can my symptoms be related to the formula I was given to drink?

Yes, diarrhea can be a harmless side effect of the iodine solution you drank prior to your CT examination. The iodine solution is thicker than water. Therefore, the fluid may remain in your bowel rather than being absorbed by your body. This type of diarrhea is usually very mild and should resolve within a day or two, after all the iodine has been excreted.

The iodine formula, or oral contrast, is very helpful in the evaluation of your CT scan. It helps to outline the bowel, which can provide information about the condition of your gastrointestinal tract, as well as to increase the contrast between the bowel and other organs and tissues in your abdomen and pelvis.

What happens if the dye "leaks" from the injection site?

Although this does not occur very often, it is possible that the IV needle used to inject the dye may not be properly located within the vein or may become dislodged. This can result in contrast material leaking into the surrounding tissue, called extravasation. This is painful, and is usually noticed immediately by the patient or the technologist monitoring the study.

It is unlikely that long-term damage will occur. The usual treatment is warm compresses and over-the-counter pain relievers.

I have a pacemaker. Can I safely have a CT scan?

Since CT scanners use X-rays to generate images, a person with a pacemaker can safely have a CT scan.

However, a different type of test, MRI, uses a strong magnetic field to produce images. Therefore, an MRI machine can interfere with the function of a pacemaker. People with pacemakers should not even get close to an MRI scanner.

My friend recently had a whole-body CT scan, and they found some abnormalities she didn't even know about. I feel fine, but should I have a test like this to make sure that I'm OK?

The newest generation of CT scanners are called “multidetector” or “multislice”. We have one such scanner in Kaiser Fremont, and will be getting another one in Hayward. The advantage of these state-of-the-art scanners is their speed. They collect data so quickly that the entire body can be scanned during a single breath-hold. These CT scanners help doctors provide fast and accurate diagnoses for injured or critically ill patients.

However, some have pursued the use of these new CT scanners beyond the accepted medical indications, as a business venture to sell full body investigations to healthy people. There is no agreement among the medical community that whole-body imaging is necessary, or that it has a beneficial impact on the health or life expectancy of people that have the test. Most “abnormalities” that are found are meaningless to a person’s overall health. In fact, often the findings create undue anxiety and the need for multiple additional tests just to prove that there is nothing to worry about. There is some evidence that certain applications of multidetector CT scanners in high-risk populations may be of benefit. Some examples of this are virtual colonoscopy and coronary calcium screening. However, these tests are still investigational, and at present there are other, more established, tests for these purposes. Our highly trained radiologists keep abreast of the latest guidelines, and will continue to monitor the need for adopting new applications of medical technology into our practice.

A very important point to remember is that a whole-body CT scan is not without risks. CT exams, as with many other radiologic studies, involve radiation. High levels of radiation may cause cancer. The relatively low risk of developing cancer from a radiologic study that is felt to be medically indicated justifies the use of imaging when your doctor orders a radiologic test. However, whether the risk of radiation outweighs the possible benefit in a healthy person who undergoes a whole-body CT scan is questionable.