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"Is it common to always do a CT scan without dye before taking CT scan with dye? Why?"

ZocdocAnswersIs it common to always do a CT scan without dye before taking CT scan with dye? Why?


My doctor ordered a CT scan with contrast for me. In fact, he ordered two CT scans - one with and one without contrast. When I asked him if it is necessary to have both of them, i.e. if there a chance that he could make a recommendation based just on a scan with contrast (and I could do another scan later if needed), his reply was "Whenever they do CT scan with contrast, they ALWAYS do CT scan without contrast first". Is it true? Why? Doesn't it double the amount of radiation exposure, drive up the cost and is rarely medically justified? Please tell me if I miss something here.


This is an excellent question. For further information it is prudent that you discuss this with the physician ordering the test the exact reasons for obtaining a with and without contrast CT scan, but in short, the reason that some CT scans are done with and without contrast is because there are lesions that are known to "enhance" with contrast, meaning that they will show an increase in density on the imaging study with contrast administration. It is not possible to know whether enhancement has occurred unless there is a noncontrasted CT scan to compare this with. There are various CT scans performed, and contrast may or may not be required depending on what is the concern and what is being looked for. Again, because it is not clear if the CT is being done of your abdomen, chest, or brain or any other part of your body, it is impossible to know what the reason is for the CT with and without contrast as well as what the physician was looking for. I agree that it does require double the amount of radiation that a noncontrasted study would, but I would not agree that it is not medically justified for the above reasons. Please discuss this with your physician.

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