Whole-body CT screening--should I or shouldn't I get one?
If you have no symptoms of illness but are considering getting a whole-body CT screening exam, you may be thinking either or both of the following:
a. "For my peace of mind, I just want to know that I don't have any diseases now."
b. "If I have a disease, I want to know about it now so that I can do something about it."
What you may not realize is that getting a whole-body CT screening exam may not accomplish either of these goals. In particular, an abnormal finding may not be a serious finding at all. And a normal finding may be inaccurate. We will consider these one at a time below, but before we do, the good news is that, if you have no symptoms of illness, the probability is high that there is nothing seriously wrong with you--and this is true without your ever getting a whole-body CT screening exam.
Should you be screened? Like any other medical procedure, there are risks involved. Before undergoing this exam, be sure to read all the sections of this web site. Consider further that the FDA has never approved CT for screening any part of the body for any specific disease, let alone for screening the whole body when there are no specific symptoms of disease at all. No manufacturer has submitted data to FDA to support the safety and efficacy of screening claims for whole-body CT screening.
What is a screening exam?
A screening exam is a medical exam that is performed on individuals who are at risk for a particular disease or condition, but who lack any signs or symptoms of the disease or condition, to determine if the disease or condition is present. Common examples of screening procedures are:
* mammography for breast cancer in women over 40 years of age
* Pap smear for cervical cancer in women over 18 or sexually active
* colonoscopy for colon cancer in men and women over 50
* blood pressure measurement for hypertension in anyone
* measuring blood sugar for diabetes in anyone.
As the examples illustrate, screening exams are generally done to look for a particular disease or condition, and they should generally be done only when clinical studies have demonstrated that screening exams may do more good than harm.
Is CT the best way to screen for any disease or condition?
At this time, no--although there are currently in process trials to determine if:
1. spiral CT might be a useful method to screen for lung cancer in smokers of particular ages,
2. CT virtual colonoscopy is as good as colonoscopy in men and women over 50 and
3. CT coronary calcium scoring is effective in predicting heart disease.
Some diseases that do have effective treatments can be found early enough with tests other than CT. For example, though this has again become controversial, screening mammography has been shown to find breast cancer early enough in many cases to be curable, but CT has not been found to have such capability. Similar results have been found for Pap smears for cervical cancer, and colonoscopy for colon cancer. There are also diseases and conditions, other than cancer, for which early treatment, even if the disease were identified, would be no more effective than when treated later, at least with treatments currently available. And there are significant diseases that cannot be seen on CT, such as diabetes and hypertension.
When is screening beneficial?
Screening tests can be extremely beneficial, but only under the following conditions:
* when the test is for a particular disease or condition, rather than for just anything that can be found
* when the test is for a disease or condition that is curable or manageable if found early enough but life-threatening by the time symptoms arise,
* when the test can find that disease or condition early enough to be curable or manageable,
* when the test doesn't reveal too many findings that resemble the disease or condition but which in reality would not hurt you,
* when the test doesn't miss too many cases of the disease or condition,
* when the test itself doesn't harm you significantly, and
* when the treatment for the disease or condition doesn't cause more harm than the disease or condition itself.
As mentioned above, examples of such screening tests are mammography, Pap smears, colonoscopy, and blood pressure measurement. Although there are ongoing clinical studies of CT to see if there is more benefit than harm for some diseases and conditions, at this time, there is no disease for which CT has been shown to satisfy the preceding conditions.
When is CT beneficial?
CT can be extremely beneficial when a person has signs or symptoms of some particular disease or condition. CT can help to diagnose or rule out the disease or condition. Furthermore, in someone diagnosed with some particular disease or condition, CT can be extremely helpful in determining the extent of disease and in monitoring the effects of treatment. Such diagnostic use of CT in people with signs or symptoms differs from the use of CT in screening of people with no signs or symptoms. People with symptoms have a much higher probability of having the disease or condition than people without symptoms. Also, people with symptoms probably have more advanced disease than someone without symptoms, which makes it easier to find the disease on CT. The result is that in a group of people with signs or symptoms, the probability of a true finding of actual disease is much higher, while the probability of a finding of something harmless that is mistaken for disease is much lower.
What are the risks and benefits of whole-body CT screening?
Many people believe incorrectly that a medical test always distinguishes between the abnormal and the normal, or the sick and the well, or the diseased and the non-diseased. Every test does this only in some cases, and you can rely on the fact that every test, including CT, gives incorrect results a certain portion of the time.
To understand the risks and benefits of whole-body CT screening, it is perhaps easiest to divide the results of the exam into two possible outcomes, normal and abnormal.
If your CT examination result is interpreted as normal, either
* you may really have nothing significant wrong with you, or
* you may have a hidden disease that fails to show up on a CT image or is missed or misinterpreted by the radiologist.
If your CT examination result is interpreted as abnormal, either
* the abnormal interpretation may be incorrect or you may have nothing significant wrong with you, or
* you may really have a life-threatening disease for which there may or may not be a cure and, if a cure exists, there may or may not be time to do something that can cure it.
Consider these possibilities one at a time. If you receive a normal report and there really is nothing significant wrong with you, then you might go away with peace of mind, but you will have exposed yourself to radiation and its associated risks. The radiation dose, in terms of effective dose, from a CT exam can be several hundred times that of a chest x ray. Not only might this amount of radiation exposure give you a slightly increased chance of getting cancer, but also, if large numbers of healthy people now start to receive radiation exposure from whole-body CT screening for questionable benefit, the overall effect on public health could be detrimental. This would be detrimental all the more so if people were to receive this examination repeatedly, on a regular basis.
If you receive a normal report but a life-threatening disease is really present, then you will have received false reassurance that could interfere with your recognizing symptoms or getting appropriate screening tests later. In addition, you will have exposed yourself to radiation from which you derived no benefit.
If your CT screening result is interpreted as abnormal and there really is nothing significant wrong with you, then you may be subjected to still further tests or treatments, all of which have their own risks. For example, further tests may bring about additional radiation exposure and the small chance of toxicity from contrast material needed for visualization, or the bleeding, infection, and potential disfigurement associated with biopsy or exploratory surgery. And treatments may include surgery, radiation, chemotherapy, or medicines, each with its own small risks of injury, toxicity, or even death. The surprising fact about a CT interpretation of abnormality when there is nothing significant wrong is that it is far more likely to happen to you than the finding of any actual life-threatening disease, since the likelihood that you actually have any deadly disease is so small to begin with.
Finally, if your CT is interpreted as abnormal and the abnormality represents an actual hidden, life-threatening disease, then you may have benefited. The benefit will be real only if:
* the disease has an effective treatment, and
* it is found early enough for you to benefit from this treatment.
Many life-threatening diseases do not have effective treatments, or, if they do, the period in which the treatment might have worked may have passed already.
In summary, when possible risks are compared to the possible benefits, the harms currently appear to be both far more likely and in some cases may not be insignificant. These harms are: (1) radiation exposure which has a small risk of cancer induction for an individual CT procedure, and (2) the possibility of either a false finding of an abnormality or a true finding of an insignificant abnormality, either of which could lead to further harm.
So, if you are apparently healthy, the good news is that the probability is already high that there is nothing seriously wrong with you, without you ever getting a whole-body CT screening exam.
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|Publication:||Pamphlet by: U.S. Food and Drug Administration|
|Date:||Apr 3, 2002|
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