Medical Screening Tests

     In previous blogs I have discussed the rationale (or lack thereof) for certain tests, for certain questions in the medical history, and for the annual physical exam. Here I wish to discuss a more difficult question: the reason for performing certain screening tests. Again, let me emphasize that I am only talking about how a given screening test benefits the individual, and not how performing the test on the individual would benefit society. Whether or not an individual patient should submit to (and possibly pay for) a test that the doctor knows would only benefit society and not the patient is an interesting philosophical and ethical question, but that discussion is outside the scope of this blog. Needless to say the question of cost-effectiveness will not enter into my discussion, since if I am restricting myself to the direct benefit to the patient, the ultimate cost to society should be outside my purview. For the sake of this discussion, I will also assume that the test is 100 per cent accurate, with no false positives or negatives. I realize that this assumption is similar to assuming a straight line has no width, but the minute we admit the existence of errors in screening tests, the discussion has to include statistical probabilities as well as the incidence of the disease being screened for, and I am trying to keep this presentation as uncluttered as possible. I am also deliberately omitting any discussion of the optimum interval between tests, since there is virtually no hard data on this point for any test.

     The problem, of course, with this minimal set of assumptions, is that we now have a reason for doing any test for which there is a treatment that can avert morbidity or death. A chest Xray  could show unsuspected tuberculosis, a blood test could show unsuspected mercury poisoning, and an EKG could show a regular rhythm with unsuspected 2:1 block. Again, we are not interested in the probabilities of these diseases, but only with finding them. And of course if you asked the patient if he/she wanted to be tested for TB or elevated Hg+ or a cardiac  arrhythmia, the answer would be "yes" in all instances. And if you as the patient's doctor knew in advance that a certain test would demonstrate a treatable condition, you would be morally and legally wrong not to order the test. So how do doctors decide which tests to do or not to do?

     Unfortunately for the purist, this is where statistical probabilities and the doctor's diagnostic acumen and level of disease suspicion enter. Should every patient dwelling in the northeastern United States or certain other geographical areas have a western blot test for Lyme disease and babesiosis? Should every sexually active patient be tested for syphilis and HIV? Should every woman of child-bearing age receive a blood test for pregnancy before every Xray? Since at autopsy 10% of males at age 40 have coronary artery disease should every male have a stress-thallium at this age? Should everyone have a flexible sigmoidoscopy (which requires virtually no cleanout, unlike a colonoscopy) at age 30 to look for colon cancer? Shouldn't everyone have a skin test for tuberculosis? Shouldn't everyone receive an echocardiogram to look for IHSS and an abdominal USG to look for an abdominal aortic aneurysm?

     After the tests are done, we then have methodological questions: At what level of fasting glucose should we label a patient as "pre-diabetic"? At what level of fasting glucose should we start pharmacological treatment, and what glucose level should be our goal? Since the risk of stroke and heart disease increases monotonically with systolic blood pressure, at what number should we start to treat blood pressure, and to what number do we wish to reduce it? To what number should the cholesterol be lowered? If we start to treat a  patient, how often should the patient be retested? When a government-sponsored panel of doctors makes a health recommendation, why aren't we told the vote? (I am much more confident in following a 19-1 vote than a 12-8 vote.) And why aren't we told the arguments of the doctors who disagreed with  the public health recommendation the way we are when the FDA recommends approval of a drug? And do the doctors who voted against the recommendation of the majority of the panel change the way they practice medicine to conform to the recommendation of the panel, even if they think the panel is wrong?

     I hope this blog serves in part to show that there is an art of judgment in medicine. In today's topic  the judgment lies  in deciding which tests to order and which not to order. There is also another art of judgment when the test results come back: how "abnormal" does a blood test or Xray have to be in order to influence the treatment plan of the physician?

The Annual Physical

     There has been much written lately about the utility or non-utility of the annual physical exam and its associated tests. There have been articles in the New York Times, the Annals of Internal Medicine and the Journal of the American Medical Association, as well as statements by the National Institutes of Health, the American College of Physicians, the American Academy  for Family Practice the Canadian Medical Society, and various other organizations. Since there has never been an overall consensus, the reading public is left confused and thrown back on its own resources and preconceptions.

     Firstly, what do we mean when we say that an annual physical exam is "beneficial" to the patient? The answer to that question depends in part on who we ask, and in part on how we measure "beneficiality". Do we ask the opinion of the patient, the doctor, a medical organization, a patient organization, an insurance company, or the government? Is an annual physical exam and its associated tests beneficial if it saves the patient's life,  or if it reduces future morbidity, or if as a result  the patient functions with more physical and/or mental energy? And what of the sense of well-being that a patient feels when he/she is told that the results of the annual exam were perfectly normal? Do we discount that feeling because there is no way to measure and quantify it? Isn't there  value in reassuring a patient that his/her aches and pains are not the symptoms of a serious disease? What if the meat of the annual exam lay in one question that the physician answered for the patient, or one medical misconception that the doctor cleared up and thereby enabled the patient to avoid a future medical problem?

     In previous blogs I have listed questions that should be asked at the annual physical, and which tests I think are medically beneficial and which are not, along with my reasons for the tests. One could make a case that just making sure that the patient received an annual flu shot is enough reason for an annual physical. One could also make a case for measuring blood pressure, since there is plenty of clinical evidence that treating hypertension with a regime that includes a diuretic reduces the patient's risk of a cerebral stroke. There is also an argument for annual testing for infectious diseases that can be treated, such as tuberculosis, syphilis and AIDS. What of the benefit to society when I ask a patient if he/she has trouble reading street signs at night while driving, and then suggest seeing an ophthalmologist if the answer is "yes"? I gloss over the obvious comments a physician would make to the patient about losing weight, stopping smoking and getting more exercise (although a recent study showed that 10% of the patients who exercise damage their health by doing so, two studies  published in Lancet showed that overweight people with a BMI between 26 and 29 had better odds of surviving a heart attack, and two European studies demonstrated that smokers have a reduced incidence of Parkinson's disease). And should I encourage teetotalers to have a daily glass of wine since every study shows that this nutritional intervention improves mortality?

     One fact that is never mentioned in all the discussions of annual physicals is state law: in every state it is a violation of "good medical practice" for a doctor to renew a prescription if the patient has not been seen  within the previous 12 months (and more frequently for DEA-controlled drugs, which includes sleeping pills and tranquilizers). By age 40 almost every patient is taking at least one prescription drug, and therefore needs to be seen annually. And for those only taking over-the-counter supplements, their regime should also be reviewed annually to keep them from consuming OTC drugs that might be harmful----e.g. we now know that daily doses of Vitamin E increases your risk for having a heart attack.