Why doctors can’t screen patients for every disease

I had a patient once who wanted an exercise stress test even though he had neither symptoms nor risk factors to suggest the presence of coronary artery disease (such as chest pain with exertion).  I argued vociferously against it.  However, extenuating circumstances (not relevant here) prompted our mutual decision to go ahead with it anyway.  To our surprise and dismay, it came back positive.

When to screen

Given the amazing advances in medical technology in the last four decades or so, the American public has come to expect and believe that if a test exists for a disease, it should always be done.  Nothing, however, could be further from the truth.  The decision about which tests to perform on which types of patients and when to perform them actually requires a complex calculation.

First, we must distinguish between a screening test and a diagnostic test.  Often a single test can be used as either, the difference arising from the circumstances under which it’s performed.  So, in my patient who had no symptoms or risk factors to suggest the presence of coronary artery disease, putting him on an exercise treadmill by definition represented a screening test:  that is, an attempt to identify the presence of a disease before it produced symptoms.  Were he to have complained of chest pressure while climbing stairs, in contrast, putting him on a treadmill would have represented a diagnostic test:  that is, an attempt to confirm or exclude a disease that had already manifested symptoms.

Why don’t we screen everyone for every disease we can?  First:

  1. The disease must represent an important health problem.  We could, for example, screen everyone for mononucleosis.  But given that 90% of the population has already been infected without ever knowing it by the time they leave adolescence (and having had it are now immune to having it again), no reason exists to screen for it.
  2. An effective treatment for the disease must exist.  Scientists are working on tests to detect Alzheimer’s dementia in its early stages.  But because we still have no effective treatment for it, screening for Alzheimer’s at this point makes little sense.  In fact, doing so may cause real harm—the harm that comes from knowing you’re highly likely to develop a fatal disease for which there exists no cure.
  3. A latent stage of the disease must exist.  If no such stage exists (e.g., asthma), no opportunity to identify the disease before it becomes symptomatic exists.  If the first time it becomes possible to identify the presence of a disease is only once it becomes symptomatic, why bother attempting to screen for it?

Second, putting aside the issue of affordability, specific criteria exist that must be met before any test can be considered appropriate for use in screening effectively and safely.

  1. The screening test must be able to detect the disease in the latent stage early enough to affect outcomes.  The key isn’t just catching the disease in the latent stage but catching it before what’s known as the critical point—the point beyond which, even though the disease hasn’t yet produced any symptoms, it’s no longer curable.  A case in point:  studies have been done showing that obtaining screening chest x-rays in patients lacking signs or symptoms of lung cancer does indeed identify asymptomatic cancers earlier than if the x-rays weren’t performed—but still too late to affect the rate of cure.  Interestingly, a recent study suggested that performing CT scans as a screening test does catch at least some lung cancers early enough to increase the likelihood of cure (by about 20%).  This is probably because CT scans can pick up much smaller tumors than chest x-rays can, presumably increasing the likelihood of identifying the presence of lung cancer prior to the critical point.
  2. The risk of false positives must be acceptably low.  A false positive result occurs when the test says you have a disease that you really don’t.  The likelihood that a test is right when it says a patient has lung cancer (what’s called the positive predictive value of a test) turns out to be greater in smokers because smokers have a higher risk than non-smokers of getting lung cancer.  (This is because the more prevalent a disease is in a given population, the more times the screening test will actually find the disease it’s designed to detect.)  This matters a great deal because once a screening test says a patient has a disease, to confirm the presence of the disease progressively more invasive tests and procedures are often required, which exposes patients to progressively greater risks of complications.  For example, a single chest CT poses little risk to anyone (the rate of contrast reactions is quite low in the general population), but the lung biopsy or wedge resection that will likely follow a positive scan are invasive enough to pose significant risk.  And though uncommon, the following scenario can occur:  a patient has a positive CT, gets a biopsy or wedge resection of her lung, and develops a complication that ultimately leads to her death—only to have the pathology on the tissue taken from her lung turn out to be benign.  The risk of a similar scenario prevents us from recommending exercise treadmill tests, like the one my patient had, for people without symptoms or risk factors for coronary disease.  False positive treadmill tests happen frequently in those patients, often leading to cardiac catheterizations, which carry a small but definite risk of death—a risk that’s only justified when the suspicion of a false positive result is sufficiently low.
  3. The risk of the test itself must be acceptably low.  Blood tests represent almost the lowest-risk tests we have (the needle stings and some people get woozy or faint, but that’s about it) other than physical exam maneuvers.  A colonoscopy is slightly more invasive and carries a slightly higher risk (colonic perforation is a catastrophic event but happens rarely).  A cardiac catheterization, on the other hand, is distinctly more invasive (the puncture is arterial rather than venous) and therefore carries a distinctly higher risk, one high enough to disqualify it as a screening test altogether.

The number of tests that meet these criteria are far fewer than most people realize.  Further, the utility of many that do satisfy them remains controversial.  Consider the PSA test, a blood test used to identify asymptomatic prostate cancer.  While it satisfies the three criteria listed above, the more studies that are done on it the less clear we become about what number actually represents a positive result.  It used to be a PSA below 4.0 was thought to effectively rule out the presence of prostate cancer.  Then we found a small but significant minority of patients with PSAs between 2.0 and 4.0 actually had it.  Now we’re thinking this may also be true for patients with PSAs between 1.0 and 2.0.  (To explain how researchers figure out what “normal” is for any given test would take an entire post in itself.)

In the end, convinced my patient’s treadmill test represented a false positive result, rather than take him to cardiac catheterization, I put him on a treadmill test again, this time using nuclear imaging (an addition that conveys a negligibly increased risk but far greater sensitivity), which, thankfully, was negative.  We both heaved sighs of relief, and he became convinced that just because we can test for something doesn’t mean we always should.

Alex Lickerman is an internal medicine physician at the University of Chicago who blogs at Happiness in this World.  He is the author of The Undefeated Mind: On the Science of Constructing an Indestructible Self.

Comments are moderated before they are published. Please read the comment policy.

  • http://brent.kearneys.ca Brent Kearney

    All of the other factors aside, this one:

    2. An effective treatment for the disease must exist.
    Scientists are working on tests to detect Alzheimer’s dementia in its early stages. But because we still have no effective treatment for it, screening for Alzheimer’s at this point makes little sense. In fact, doing so may cause real harm—the harm that comes from knowing you’re highly likely to develop a fatal disease for which there exists no cure.

    … just seems wrong. Must we wait for big pharma to sell a pill for a disease before we can say that something can be done about it?

    There is a constant stream of new scientific discoveries in brain health and other areas which can guide the choices that people make, to attempt to steer away from developing a disease. The pros surely outweigh the cons — but more to the point: shouldn’t the individual get to decide 1) whether to test, knowing that they may have to live with the bad news, and 2) if the test is positive, whether to try therapies or lifestyle changes that are not (yet) endorsed by big pharma?

    • Dave Miller

      Regarding “therapies or lifestyle changes that are not (yet) “endorsed” [emphasis mine] by big pharma,” there are few areas in which folks are being raped, plundered and pillaged more than this. There is a never-ending mass of “snake oil salesmen” all over the internet, in the book stores and on TV. People are looking for ways to control things that can’t be controlled and being told that “big pharma” is just trying to rip them off. In the end, it is often the “alternative treatments” that are a ripoff, not only robbing the patient of their hard-earned money but often-times giving them false hope (which is perhaps more damaging in the end).

      • Lil A

        As can be seen in the case of Kevin Trudeau, who was banned from selling products on TV for life after he was found out to be ripping people off. He now claims, in all sorts of books that are covered by the first amendment, to heal diseases that they may not necessarily heal. People buy these books and go off their medicines in hopes of curing what they have. A few of his “miracle cures” have been the calcium cancer cure, claiming that taking calcium will cure cancer, rather than radiation or chemotherapy. Another one has claimed that a combination of special herbs can cure diabetes. I’m sure that we all know what can happen when a diabetic goes off of insulin. It’s downright dangerous, yet people still believe that these “miracle cures” actually work.

  • Skeptical Scalpel

    For an in-depth look at this important subject, you should read “Overdiagnosed” By Gilbert Welch et al. I just finished reading it. He makes a number of cogent arguments against most screening tests.

  • http://fertilityfile.com IVF-MD

    It boils down to this. Suppose a woman is deciding on whether or not to have a mammogram. Let’s say it costs about $500 for the study and the reading. And let’s say you believe the US task force on preventative service estimate that there is about a 1 in 2000 chance that this test will save her life. Given these numbers, an intelligent person can make a decision of whether or not she wants to spend the money to get the supposed value. The same type of analysis can be done for other tests as well.

    In my specialty, we have a specific screening test which we offer but which the majority of people choose not to have, namely genetic testing. We have the technology to test embryos ahead of time and make sure with 99%+ accuracy that a woman will not get pregnant with a fetus that has Trisomy 21, regardless of her age. The conversation typically begins with the patient expressing fear of having a child with chromosomal abnormalities. Then I explain the costs, benefits, risks of the procedure. OK, technically, this is a high sensitivity test and not a screening test, but the principle still applies. Then the patient makes her decision, which is usually NO. By teaching an intelligent person the costs, benefits and risks, they can better make a decision for themselves. If they feel that they can’t decide, then I will give them my opinion, which is usually not to get it.

    • Diora

      Suppose a woman is deciding on whether or not to have a mammogram. Let’s say it costs about $500 for the study and the reading. And let’s say you believe the US task force on preventative service estimate that there is about a 1 in 2000 chance that this test will save her life. Given these numbers, an intelligent person can make a decision of whether or not she wants to spend the money to get the supposed value.

      An intelligent person should also consider that after about 10 years of annual mammograms her risk of having at least 1 false positive is between 25 and 50% (or whereabouts) and that there is also a risk of overdiagnosis.

      Dollars and cents aren’t the only things to consider here.

      • http://fertilityfile.com IVF-MD

        Absolutely. In previous posts, I spoke of the “costs” of screening as including more than just money but also pain, inconvenience and the consequences of false positives such as unnecessary surgery.

  • Alan

    Gilbert Welch’s prior book, “Should I be Tested for Cancer,” makes the case that the downsides of testing are certain, while the benefits are mostly unclear. To round out the set of considerations, one would have to be cognizant of the number of false positives, for instance, in mammography results (over 50% in some age cohorts), and the psychological as well as monetary costs of distress and follow-up testing in light of such false positives. The age of the woman’s in question would also come into play. Such decision making is asking a lot of a boundedly rational human brain, even assuming a high g intelligence.

  • http://www.ama-assn.org/amednews/2011/01/31/gvsa0131.htm AustrianSchool

    Doctors cannot prevent death in kids because of government intrusion into their field. e.g. fines and prison sentences handed down to docs in Florida for counseling parents about gun safety.

  • Finn

    I also disagree about 2. An effective treatment must exist, but not for Brent Kearney’s reasons. I think the value of screening for diseases like Alzheimer’s without an effective treatment is allowing the patient time to plan for their own care. Not everyone would, and I don’t think we need to screen everyone for Alzheimer’s, but I can see how the knowledge would be useful for some people. There are lots of people currently living with the knowledge that they’re going to develop an incurable, fatal disease because they’re infected with HIV, carrying the gene for Huntington’s, etc., and not all of them are devastated by this knowledge. Just as some people with a family history want to be tested for Huntington’s and some don’t, some people would want to be screened for Alzheimer’s while they’re still with-it enough to make some plans or do something they always wanted to do.


    Please submit your artilcle to Consumer Reports, Readers Digest and or as many public forums as possible. In our capitalist society we are driven by our consumers and unfortunately they receive most of their education from unreliable sources.

  • http://www.BocaConciergeDoc.com Steven Reznick MD

    This is a no win situation. We used to screen smokers for lung cancer with an annual chest x-ray. Every year half a dozen patients in our two physician practice were found to have changes in their films before they were symptomatic and were sent for life saving chest surgery. The radiation exposure for all those with no disease, the cost to the system and the few cases found per x rays taken made the project totally cost inefficient. Try explaining that to the patient who just had their life saved or to their friends and loved ones. Yes there were instances where we found a nodule that led to an evaluation and it turned out to be benign. These patients experienced the risk of the interventional biopsy plus the anxiety and cost which made finding a false positive horrible for the patient, their family and friends. There is no easy answer to this question. I believe medical science is trying to determine through scientific studies what works and what is snake oil. When you are dealing with a highly emotional issue like severe health problems consumerism often trumps common sense and scientific findings. As a physician our role is to explain and teach the difference between fact and folly. With insurance companies paying many of the expenses , patients often go with the emotional rather than the science based decision.

  • Angela Caffaratti, MD

    I find that the people who make healthy choices want “just to be sure” and people who make less healthy choices don’t want any screening even though they are at higher risk. This is just a generality with many exceptions. It is hard to convince people that we can never be sure and it is hard to convince people to get colonoscopies, which are clearly beneficial, because of perceived inconvenience or embarrassment. It is also hard to explain that more can be worse when the Today Show markets costly and dramatic care with a win-win spin. My hats off to IVF-doc whom addresses this well. Informed consent is inherently difficult.

  • buzzkillersmith

    Explaining Bayesian statistics to patients is a job for Sisyphus. Most doctors don’t even understand it and even ones that do act as if they don’t.
    The vet just convinced us to do a “geriatric panel” on our 12 year-old dog. His LFTs came back high, although he has no clinical evidence of liver disease. Irony.

  • http://www.epmonthly.com/whitecoat WhiteCoat

    I agree with buzzkiller.

    People do a plethora of things in our society without being explicitly told of the risks and benefits, number needed to treat, and complex calculations in life expectancy involved in doing so: Smoking, illicit drugs, visiting too many doctors, visiting not enough doctors, driving without a seat belt, driving too slow, driving too fast, driving really too fast, eating fast food, eating healthy, eating salt, drinking too much diet soda, drinking too much water, etc, etc, and so on.

    We need to deregulate the medical system so that blood and radiologic tests are available to the general public. Then if the wife of Joe the Plumber wants to spend $500 every week on a mammogram, let her.
    If she wants to pay a doctor to explain the risks and benefits of obtaining the test, before draining her bank account, great. She’ll probably save money.
    Ultimately the decision on whether to obtain the test should be left up to the patient, not the doctor. If a test comes back with an equivocal result, then the patient determines whether the cost of the additional testing is worth any potential gains from having the testing done.
    We do this in every other aspect of society, why should medicine be any different?

    Imagine all of the “defensive medicine” dollars that could be saved by putting patients in control of their health care spending and doing away with liability for doctors that “fail to order a test” and miss the needle in the haystack diagnosis.

  • Jackie

    The most cost-effective way is probably patient education and better communication.

    My husband has been prescribed high blood pressure medicine since his early 20′s. He used to be a long-distance runner, but had to quit because of ‘runner’s knees’. He then resorted to walking. One day he came home early from his walk and described to me the strage sensation he experienced briefly during his walk. It was not the first time, but it was much more severe than he’d experienced before. I looked up the ‘Self-dianosis Symptom Charts’ in the AMA Family Medical Guide and correctly ‘diagnosed’ him as having ‘angina’. A stress test and then angiogram confirmed our suspecion and hubby underwent a angioplasty within a month. Two stents were placed for the three areas that had blockages of 95%, 85%, and 75%.)

    I’ve had two brain (tumor) surgeries, two breast cancer surgeries, and a prophylactic hysterectomy/oophorectomy since 1990. Every one of my family doctors had thought I was hypochondriac – until I ‘proved’ them wrong. The breast cancer recurrence was not caught (for almost 4 years) until I requested an early mammogram through my breast surgeon.

    Screening tests are only as good as the persons who read/interpret them.

    Jackie, PP (Professional patient)

    • Lil A


      I know precisely what you mean. I have diagnosed myself a few times in the past before, with the first one being at 13 for Endometriosis. Doctors never believed that I had it because textbook Endometriosis is usually diagnosed in women much older than me. Besides, I didn’t have my period long enough for the lesions to grow, right? Wrong! The first doctor I went to wanted to put me on prescription medications, trying a wait-and-see approach to see if my symptoms improved. Being prescribed Vicodin for menstrual cramps after Darvocet (another narcotic) became ineffective for me after 2 months should have surely sent up red flags. He didn’t want to do more than prescribe, so my mom found a doctor that would do a laparoscopy. Guess what? It turns out that I did have Endometriosis and Adenomyosis. I was immediately put onto hormonal treatment to treat it, and went through hell for the next few years afterward.

      The other time I had lower right quadrant pain, and I typed my symptoms into Google. At 1 in the morning, I had a definitive diagnosis of either appendicitis or ovarian cyst. I ended up going to the ER later that day. The diagnosis? Acute appendicitis. I underwent emergency surgery that night to have my swollen appendix removed before it burst.

      I believe that patient education is important in good care and advocate for patients to research what they have and to work with the doctor on how to treat what they have. However, the danger comes when the patient starts thinking that they will dictate how they will be treated due to the newfound knowledge they have gained, and they forget that they aren’t the ones that have gone to medical school and have gone through many years of internship, fellowship and stuff like that. They think just because they read the article on WebMD that they are an expert in what they have. This is not necessarily the case.

      I believe that an attitude of humility is best employed by both physician and patient, as no person on earth knows everything about everything. There is still much to explore, and an open mind and humility can be of significant use in medicine.

  • Jackie


    My sister-in-law is a nutrition professor. She (and everyone else) thought my Mother-in-law was pretty much a ‘goner’ when all the family members gathered around the living room in the nursing home. Then Mother-in-law ‘perked up’ (probably experienced a ‘natural bypass’) and lived another 6 months.

    Two years later, Sister-in-law called my husband that my Father-in-law was ‘dying’. While she was taking the 4-hour drive back to her house to pick up clothing for the ‘funeral’, my husband and I went stay with Father-in-law and realized his dlirious state was most likely caused by urinary tract infection. EMS was called and he was taken to the hospital in our town. Father-in-law has been back to ‘normal’ and still drives himself to the hospital by himself for regular check-up even as an 87-year-old.

    I reminded Sister-in-law one time about my own health problems/triumps when she was using the term ‘quality of life’. Who’s to decide what ‘quality of life’ is acceptable to the person? “Who’s life is it anyway?”

Most Popular