If you’re confused about what screening tests you need, you’re not alone. Screening seems like a no-brainer. Catch a disease early and deal with it before it causes trouble. Unfortunately, the reality of screening tests is not quite that simple.
Recommendations for screening take a number of key factors into account:
- how common a disease is
- the sensitivity of the tests available to accurately identify disease
- the ability of the test to separate unimportant abnormalities in healthy people from findings associated with disease
- the safety of the test
- the discomfort of the test, and
- cost
Take total-body CT scans as an example. Not long ago, there was a lot of talk about using total-body CT scans to screen for cancer. There were even advertisements suggesting that you “buy your loved one a total-body CT scan for Christmas”! You can go online and find websites hawking total-body scans to look for asymptomatic, life-threatening diseases in their most treatable stages. Some places even offer bargain rates: one for $425, two for only $800!
If the total-body scan is so terrific, why wouldn’t your doctor order such a “life-saving” test? There are good reasons. Full body scans have not been shown to be effective screening tools for people with no symptoms or risk factors. No studies are available to show they save lives. The scans often show minor abnormalities (we call them incidentalomas) that lead to many other tests, including biopsies and other invasive procedures. They also subject people to a lot of radiation, not to mention needless worry while incidentalomas are being checked out. Put simply, there just isn’t yet evidence to support the use of the total-body CT scan as a screening tool.
Choosing screening testsWhat makes a good screening test and how is it chosen? How do doctors decide what is appropriate preventive screening for someone?
First, you need to choose the disease and the population group to screen. The disease has to be serious, and fairly common in the group of people you will screen. For instance, we don’t screen 18 year olds for breast cancer-- the disease is much too rare in that age group to justify screening. It would lead to many false-positives (when someone has a positive test but in fact they don’t have the disease), which could then lead to major complications as we follow up on the results.
It also does not make sense to screen patients for very minor problems -- so we don’t screen for hangnails or sunburn, for example. Generally, only conditions that pose a significant threat to health are included in screening.
If we are to screen for a particular disease, we need to have an effective, safe and cost-effective treatment if we find that disease. Otherwise, it does not make sense to do the screening. After all, what’s the use in knowing you have a disease you can do nothing about?
Once you have chosen the disease and the population, you have to look at the screening tests available and make sure one is good enough to use. Screening tests are not perfect. They can have false positives and false negatives (when someone does in fact have the disease but the screening test misses it). A false-negative screening test may falsely reassure a person, and it may actually delay diagnosis and effective treatment. A good screening test should have few false positives (spoken of as a highly specific test) and few false negatives (a highly sensitive test). It should also save lives or improve quality of life.
We now use the results of scientifically valid studies to help determine whether a screening test meets these important criteria. There are also organizations that collect information and design guidelines to help doctors answer questions about screening. The U.S. Preventive Services Task Force is an independent panel of experts that reviews the scientific evidence for a range of preventive services including screening. Its recommendations are considered the “gold standard” for clinical preventive services. Other organizations, including the National Cancer Institute, the American College of Physicians, and the American Cancer Society also make screening recommendations.
As a result, healthy, low-risk, non-pregnant adults are usually advised to have a limited number of screening tests, those for which there is evidence of significant benefit. Commonly recommended screening tests include:
- colonoscopy
- lipid profile (including cholesterol)
- mammography
- pap smear
- prostate specific antigen (PSA)
When I first started practicing medicine, doctors screened patients without much scientific backup. We just did whatever seemed to make sense. But that has changed--now we use well-designed studies to focus our efforts and our health care dollars to help our patients live healthier and longer lives.
Do you have questions about specific screening tests? Post them here, and I will try to answer some of them in future blogs.
| Colon cancer is one important disease that has a number of tests that screen for it. One such test is a colonoscopy, which is described in the below image.
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Diana Post, M.D., is an Assistant Professor of Medicine at Harvard Medical School and a practicing internist at Brigham and Women's Hospital in Boston, MA. She is also a rheumatologist.
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Comments: 30
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Could you please address the tests necessary to check endocrine function, this seems to be a growing issue amongst my clientele - with adrenal failure, thyroid malfunction, blood sugar issues, etc...
Why are you even awake during the colonoscopy? Here in Chico, California being awake is an option, but I would never do it awake.
Well done and easy to read for someone like me with no medical background.
There is at present very little evidence to support the general screening of patients for "endocrine" disorders including adrenal disease and thyroid disease. If someone has a clinical picture suggestive of a specific problem, then I would do the appropriate diagnostic testing to try to confirm or rule out the problem. But that is not "screening" the general population.
There is evidence to support screening of certain groups in the population for diabetes. Pregnant women are screened for "gestational diabetes" which is a form of diabetes that can adversely affect the pregnancy.
Routine screening for type I ( which used to be called "insulin-dependent" or "childhood" diabetes) is not recommended. There is no accepted treatment for the early, asymptomatic phase of this type of diabetes. So early identification would not lead to treatment that might change the course of the disease.
On the other hand, type 2 diabetes (which used to be called "adult" or non-insulin dependent diabetes), is a good candidate for health screening. The number of people in this country who have undiagnosed disease is very high. We have blood tests which could be used for screening. And there are accepted treatments and recommendations for people with early Type 2 diabetes before someone is symptomatic. Most groups now recommend screening either the entire population over 45 years old, or the screening of certain high-risk groups. Risks for diabetes include obesity, a family history of diabetes, inactivity, abnormal blood fats, high blood pressure, and being a member of certain ethnic or racial groups including Hispanic, Native American and Pacific Islanders.
However, it has not yet been shown that early detection of diabetes by screening large populations actually improves outcomes of people found to be diabetic. But there is evidence to suggest that this may be true.
Yes! it is time and you should have a physical and schedule a colonoscopy. Colonoscopies can save lives! And don't forget mammograms and other appropriate screening with your physical. Good luck!
I am sorry you had such a difficult time with your colonoscopy. Although there are several ways to screen for colon cancer, currently the most frequently recommended is colonoscopy. It is the only screening test that allows both diagnosis and therapy at the same time. Polyps found during colonoscopy may be removed during the test, eliminating the need for additional procedures. But colonoscopy can be difficult to do and requires sedation. Most people getting a colonoscopy get "conscious sedation" with intravenous medication during the procedure. This really makes the test fairly easy for most people. Did you get conscious sedation? If you did, you might not have been given enough. If not, then that might be the solution next time.
Very rarely, patients are "put to sleep" for the test. General anesthesia adds to the difficulty and risk of the procedure, so generally it is not used except in special circumstances.
A newer test, the virtual colonoscopy, may turn out to be a better screening test for colorectal cancers than colonoscopy. Virtual colonoscopy is an x-ray test based on a CT scan. It does not require sedation and has almost no risk of perforation. Unfortunately, polyps cannot be removed during a virtual colonoscopy test. If a polyp or growth is seen, the patient then needs a conventional colonoscopy. At this time, no national organization recommends using the virtual test in place of the colonoscopy. But this may change. And certainly, if you are unable or unwilling to have another colonoscopy in the future, ask your doctor about a virtual colonoscopy.
In addition, new tests are being developed to help screen for colorectal cancer. One involves DNA testing of stool samples. Cells from the colon that are found in the stool can be tested for abnormal DNA indicating cancerous changes. This may be another useful way to screen for colon cancer. It is still in the experimental stage, however, and is not available at present.
2. My grandma, or at least the woman who raised mom and we can't prove that this is not my grandma, had breast cancer and recovered.
3. My other grandma on my dad's side, died of some sort of bone cancer.
4. Mom's last pap smear showed spots of some sort. Not sure what.
Reasons I haven't gone:
1. Lack of cash!!
2. Lack of time!!
3. I have no patience to wait at the charity hospital system.
So I know, you being a doctor, will have a very stern lecture for me, go ahead, say it. I am here to listen.
I remember many years ago an eminent colleague in public health arguing that cervical screening was not an effective use of scarce resource given the number of lives saved for the investment. This was pre liquid based cytology so the situation has probably changed.
Would like your observations please.
You have explained the basics of how screening tests work, i.e. by the severity of disease, its occurrence within a population, and whether screening will lead to early treatment for a significant number of patients. However, patients are told to discuss the appropriate timing of screening tests with their own physician, based upon their own risk of developing the disease. Further, due to the prevalence of general health information available from the mainstream media and on the Internet (provided without clarification of how it should be applied) people hear about unfamiliar diseases. When they hear that certain people have been diagnosed with these diseases, they think that others should be tested, too.
Perhaps the confusion lies in not understanding that screening tests involve looking for a disease in general populations of patients (who may or may not have symptoms) and diagnostic tests involve looking for a cause when a patient goes to his/her doctor with specific symptoms. If patients understood the difference between these two things, and that there is now more evidence supporting the benefits of certain screening tests for serious diseases, we might see a higher rate of compliance among patients who would benefit from screening.
Clarification of these things might also assist patients in establishing a dialogue with their doctors regarding their current and long-term health needs. It should also be noted that a lot of research is being done to find more precise screening tests for a number of diseases. As the sensitivity of the screening tests improves, the value of screening groups of patients will increase. In my opinion, widespread comprehension of the value of preventative measures, along with appropriately applied routine screening, could significantly reduce the number of people suffering from a wide variety of diseases.
That is a good suggestion – sorry I did not include that information. Some current screening guidelines which I use:
[ note that different organizations have slightly different recommendations – these are mostly from the United States Preventive Services Task Force]
Breast cancer screening: Mammography starting at age 40 for average risk adult women with yearly or every-two-year mammograms
Colorectal cancer screening: colonoscopy beginning at age 50 for average risk adults
Cervical cancer screening: pap smears for women younger than 65 who are or have been sexually active beginning at age 18-21 through age 65.
Chlamydia infection screening: Sexually active women 15- 25, others who are at risk.
Abdominal aortic aneurysm screening: men who smoke and are between 65 and 75
Hypertension screening: blood pressure measurements for adults over 18
Hyperlipidemia screening (cholesterol profile): for average risk, men over 35 and women over 45
Osteoporosis screening: Bone density measurement for women over 65 or younger with risk factors.
hope that is helpful...
That is a very interesting question. I am not an expert in the field of international health and screening. That said, I think different recommendations from different countries sometimes reflect financial realities – how much do screenings cost, and how much does it cost to save one life. Different countries budget or pay for this type of service in different ways. Some countries have more centralized health systems, with the government footing the bill for screening, and may tend to look at these issues differently.
Of course, genetics plays a big role in people's risk for disease, as does lifestyle and diet. So populations in Europe, the US or other countries have different risk profiles. That might explain some of the differences in recommended screenings. Probably this does not explain all the differences you mention.
But I still think that there is good evidence to support the use of colonoscopy for colon cancer screening rather than using stool samples for blood. I don't think it is the "ultimate" answer, however, and hopefully easier, cheaper and less invasive tests will be developed and validated. And I certainly think doing pap smears to screen for cervical cancer has been shown to be a reasonable use of resources.
Studies have shown that the incidence of celiac disease (also known as sprue) in Europe ranges from about 1 in every 100 to 1 in every 250 people. Studies in this country have shown similar findings. Most people had nonspecific intestinal symptoms, and most were undiagnosed when screened.
There are clearly potential benefits of identifying people with celiac disease: reversing unrecognized nutritional deficiencies, correcting intestinal symptoms including diarrhea, improving general well-being and reducing the risk of certain malignancies. However, it has not yet been shown that screening for asymptomatic or undiagnosed celiac disease improves outcomes. We do not know whether people identified in a screening program will comply with the difficult diet that is the mainstay of treatment. Only if people identified as having celiac disease follow this very strict diet would benefits follow. It is not clear if people with few or no symptoms would actually go along with the gluten-free diet. So it is not yet recommended in this country that we begin screening everyone for this disease, even though we do have a good screening test and we do have an effective, though very difficult treatment. Further studies are needed.
Of course, we do test people who have symptoms that suggest that they might have celiac disease. That is different from population screening. I certainly would do the appropriate tests for celiac disease if I thought someone's subtle or obvious symptoms might be due to this disease.
I completely agree with your comments. You present the difficulties and confusions so well, I have little to add. There is indeed much confusion about "preventive screening" (when someone has no symptoms) versus "diagnostic testing" when someone has one or more symptoms or complaints. Most people have been to a doctor at some point with a complaint, and sometimes diagnostic tests are necessary to find out what is causing the problem. But as you point out, that is not "preventive screening".
I think it is also difficult to understand other public health issues as well, like "dollars spent to save one life" ---- most of us think our lives would be worth any amount of money!! Yet when decisions are made about who to screen for what disease, these concepts are factored into decisions made. Clarification of these ideas would certainly help patients have more productive dialogues with their doctors.
Thank you!
sharing the light,
Erica, the Enlightenment Advisor M.A. Transpersonal Psychology Studies Counseling
http://www.enlightenment-psych.net/ericasprofile.htm