Principles and practice of Secondary prevention cost-effective; this explains the popularity of mobile imaging vans that offer full-body computed tomography(CT)and COMMUNITY SCREENING 96 A. Objectives of Screening 196 he direct-to-consumer marketing of genomic analysis. In contrast, many entive medicine alists demand the B. Minimum Requirements for Community Screening same standards of evidence and cost-effectiveness as for 97 . Disease Requirements 197 therapeutic interventions in patients with known disease. A 2. Screening Test Requirements 198 case may be made for even higher standards. Screening 3. Health Care System Requirements 198 means looking for frouble. It involves, by definition, people 4. Application of Minimum Screening Requirements to Spe with no perception of disease, most of whom are well; there- fore great potential exists to do net harm if screening is performed haphazardly. C. Ethical Concerns about Community Screening 199 D. Potential Benefits and Harms of Screening Programs 199 E. Bias in Screening Programs 200 which is the process of searching for asymptomatic diseases F. Repetition of Screening Programs 20 and risk factors among people in a clinical setting (i.e among people who are under medical care). If a patient is for Multiple Diseases(Multiphasic Screening)201 being seen for the first time in a medical care setting, clini cians and other health care workers usually take a thorough H. Genetic Screening 202 medical history and perform a careful physical examination lL. INDIVIDUAL CASE FINDING 202 and, if indicated, obtain laboratory tests. Establishing base A. Periodic Health Examination 202 line findings and laboratory values in this way may produce B. Health Risk Assessments 203 case finding, if problems are discovered, and is considered III. SCREENING GUIDELINES AND “ good medicine” but is not referred to as“ screening RECOMMENDATIONS 203 a program to take annual blood pressure of employees of IV, SUMMARY 204 a business or industry would be considered screening, REVIEW QUESTIONS, ANSWERS, AND EXPLANATIONS ius Thereas performing chest radiography for a patient who w st admitted to a hospital for elective surgery would be called"case finding. The distinction between screening and case finding is frequently ignored in the literature and in practice. Most professional societies do not distinguish between the two in their recommendations regarding screen- Secondary prevention is based on early detection of disease, ing. We use the two terms interchangeably in this chapter through either screening or case finding, followed by treat Chapter 7 discusses some of the quantitative issues involved ment Screening is the process of evaluating a group of in assessing the accuracy and performance of screening, people for asymptomatic disease or a risk factor for develop- including sensitivity, specificity, and predictive value of tests ing a disease or becoming injured. In contrast to case finding In this chapter we assume the reader is comfortable with defined later), screening usually occurs in a communi hese concepts. The purpose here is to discuss broader publi setting and is applied to a population, such as residents of a health issues concerning screening and case finding. Chapter county, students in a school, or workers in an inau Istry. 18 provide n extensive discussion of the u.s. pr reventive Because a positive screening test result usually is not diag- Services Task Force in the clinical encounter. nostic of a disease, it must be followed by a diagnostic test For example, a positive finding on a screening mammogram examination must be followed by additional diagnostic I. COMMUNITY SCREENING g or a biopsy to rule out breast cancer. As shown in Figure 16-1, the process of screening is A. Objectives of Screening complex and involves a cascade of actions that should follow if each step yields positive results. In this regard, initiating a Community screening programs seek to test large numbers screening program is similar to boarding a roller coaster; of individuals for one or more diseases or risk factors in a participants must continue until the end of the process is community setting(e. g, educational, work, recreational)on reached. Many members of the public assume that any a voluntary basis, often with little or no direct financial screening program will automatically be valuable or outlay by the individuals being screened(Table 16-1)
CHAPTER 16 Principles and Practice of Secondary Prevention Negative Record esult Start treatmen treatment reevaluate Positive response Continue treatment Figure 16-1 The pro cess of able 16-1 Objectives of Screening Programs B. Minimum Requirements for Community Screening Programs requirements for establishing a safe, ethical Diseas ive screening program fall into the following ment to prevent Hypertension Disease requirements Screening test requirements infection and a Health care system requirements revent Change in diet and i lea net, an extensive population-wide screening program may be ina propriate. Table 16-2 outlines these requirements in four common screening programs, for hypertension, high choles Behavioral terol, cervical cancer, and ovarian cancer. as further discussed unsafe sexual in Application of Minimum Screening Requirements to Sp practices Environmental Change in occupation Chronic obstructive cific Programs sease from work in a dusty trade L. Disease Requirements Metabolic Elevated seru 1. The disease must be serious(i.e, produce significant mor- bidity or mortality), or there is no reason to screen in the first place. 2. Even if a disease is serious, there must be an effective py for the disease if it is detected of alue unless there is a good chance that detecting the
SECTION 3 Preventive medicine and public health Table 16-2 Requirements for Screening Programs and Ratings of Example Methods to Detect Hypertension, Elevated Cervical Cancer, and O Screening Method and Rating Serum Cholesterol Pap Smear Computed Tomography Requirements Reading(Hypertension) Test(Dyslipidemia)( Cervical Cancer) (Ovarian Cancer) quirements Ettective treatment exists Other diseases or conditions may be detected. est is quick to perfo est is safe Test is acceptable to participants ++++++ Sensitivity, specificity, and other operating Health Care System Requirements meets Case ng in a medical care setting ngs are ap levated cholesterol levels, with total cholesterol measurement based on a rapid screening of blood; cervical cancer, tested by Papanicolaou( Pap)smear; and ovarian cancer, tested by computed tomography(CT) scanning, Ratings are as follows: ++ good; + satisfactory; - unsatisfactory: +/- depends on disease disease in the presymptomatic stage would be followed by Screening for nditions may produce such a effective therapy. Furthermore, the benefits of detecting arge proportion esults that it would not be cost the condition in a few people should outweigh the harms are best sought in the context that occur(and accrue) to people with a false-positive of care. It is possible, however, that screening for some test, including unnecessary, invasive workups and treat- common risk factors, such as elevated cholesterol levels, may ment. For example, at present, there is no value in screen- provide opportunities for education and motivation to seek ing for pancreatic cancer because the chance of cure by care and behavior change. tandard medical and surgical methods is extremely small. The controversy around prostate cancer screening 2. Screening Test Requirements is largely about the benefits of treatment versus the pos sible harm of unnecessary treatment 3. The natural history of a disease must be understood 1. The screening test must be reasonably quick, easy, and clearly enough to know that there is a significant window inexpensive, or the costs of large-scale screening in terms of time, effort, and money would be prohibitive of time during which the disease is detectable, and a cure 2. The screening test must be safe and acceptable to the or at least effective treatment would occur. For example, colon cancer follows an established disease mechan persons being screened and to their clinicians. If the indi from small polyps in the colon to colon cancer. Early iduals to be screened object to a procedure(as frequently detection and surgical removal of a polyp in the colon occurs with colonoscopy), they are unlikely to participate could prevent intestinal obstruction and morbidit and 3. The sensitivity, specificity, positive predictive value,and other operating characteristics of a screening test must be 4. The disease or condition must not be too rare or too known and acceptable. False-positive and false-negative common Screening for a rare disease usually means that test results must be considered. an additional diffie many false-positive test results would be expected for in using screening tests in the general population is that each true finding(see Chapter 7). This increases the cost the characteristics of the screening test may be different and difficulties of discovering persons who truly are ill or in the population screened from the population for whom at high risk, and it causes anxiety and inconvenience for the screening was developed. individuals who must undergo more testing because of false-positive results. Unless the benefits from discovering 3. Health Care System Requirements ne case are very high, as in treating a newborn who has phenylketonuria or congenital hypothyroidism, it is 1. People with positive test results must have access to seldom cost-effective to screen general populations for a follow-up. Because screening only sets apart a high-risk rare group, persons who have positive results must receive
CH AP TER 16 Principles and Practice of Secondary Prevention further diagnostic testing to rule in or rule out actual proportion of cancers can be cured by the time they are disease. Follow-up testing may be expensive, time letected. Because of these problems, community screening onsuming, or painful, with some risk. With many screen for ovarian cancer is not recommended ing programs, most of the efforts and costs are in the For many screening rograms, debate surrounds general follow-up phase, not in the initial screening screening issues such as what age to start the screening, when 2. Before a screening program for a particular disease is how often to repeat the screenin undertaken, treatment already should be available for methods yield accurate results. Screening for breast cancer is people known to have that disease. If there are limited an example of a controversial screening program because the resources, it is not ethical or cost-effective to allow persons benefits seem to be less than originally hoped and risks are with symptoms of the disease to go untreated and yet associated with screening mammography. The age at which screen for the same disease in apparently well persons to begin screening women for breast cancer is particularly 3. Individuals who are screened and diagnosed as having the controversial because breast is less common in disease in question must have access to treatment, or the younger women, but often more aggressive than later in life, process is ethically flawed. In addition to being unethical, and the risks of screening (e.g., false positives)are higher it makes no medical sense to bring the persons screened (Box 16-1) to the point of informing them of a positive test result and then abandon them. This is a major problem for ommunity screening efforts because many people who C. Ethical Concerns about Community Screening ome for screening have little or no medical care coverage. The ethical standards are important to consider when an Therefore, the cost for the evaluation of the positive apparently well population of individuals who have not screening tests and the subsequent treatment(if disease sought medical care is screened In this case the professionals is detected)are often borne by a local hospital or other involved have an important obligation to show that the ben- efits of being screened outweigh the costs and potential risks 4. The treatment should be acceptable to the people being The methods used in performing any public screening screened. Otherwise, individuals who require treatment program should be safe, with minimal side effects d not undertake it, and the accomplished nothing. For example, some men may not want treatment for prostate cancer because of possible D. Potential Benefts and Harms of incontinence and impotence 5. The population to be screened should be clearly defined creening Programs ideologically useful The potential benefits of screening include reduced mortal Ithough screening at"health fairs"and in shopping ity, reduced morbidity, and reassurance. With the goal of enters provides the opportunity to educate the public screening programs to identify disease in the early, presym about health topics, the data obtained are seldom useful tomatic stage so that treatment can be initiated, the potential because the population screened is not well defined and benefits are reduced mortality for many programs. However, tends to be self-selected and highly biased in favor of some screening programs have a goal of early detection using those concerned about their health less invasive treatment(e. g,, taking a small piece of breast 6. It should be clear who is responsible for the tissue rather than removing the entire breast). Another which cutoff points are to be used for consideri potential benefit of screening is the reassurance to both indi result" positive, and how the findings will bec viduals and providers f participants'medical record at their usual plac The potential adverse effects(harms)of all screening pro grams need to be considered. Some screening pr may be uncomfortable, such as mammography, or require 0f ng preparation, such as colonoscopy (colon cleansing). Colon- Specific Pro ograms scopy also carries procedural risks(bleeding, perforation) Table 16-2 applies the previously described criteria to the results, false reassurance for patients with false-negative tests, ollowing four conditions for which community screening and costs to individuals and society from lost work has been undertaken Test errors are a major concern in screening(see Chapter a Hypertension, tested by a sphygmomanometer reading of 7). False-positive test results lead to extra time and costs blood pressure and can cause anxiety and discomfort to individuals whose a Elevated cholesterol levels, based on a screening of blood results were in error. In the case of screening for breast ■ Cervical th papanicolaou cancer, one study showed that the more screening mammo a Ovarian cancer, for which CT scan screening was consid grams or clinical breast examinations given, the more likel ered but rejected one or more false-positive results occurred. An estimated 49%of women who had undergone 10 mammograms had As shown in Table 16-2, screening for hypertension, at least one false-positive reading, equal to a false-positive hypercholesterolemia, and cervical cancer generally fulfill error rate of 6% to 7%on each mammogram the minimum requirements for a community screening False-negative test results can be even worse. Or program. Investigators have agreed that a screening program implied promise made to people is that if they are screened using CT scans to detect ovarian cancer in the general popu- for a particular disease and found to have negative results, lation fails at two critical points. First, the yield of detection they need not worry about that disease. False-negative results is low. Second, as numerous studies have shown, only a sma may lead people with early symptoms to be less concerned
O0 SECTION 3 Preventive medicine and public Health Box 16-1 Screening Controversies: "Are you really saving Lives? And how much worry and lost quality of life Breast cancer and prostate cancer in particular illustrate the chal- the improvement in mortality in women between age 40 and 49 was lenge in weighing evidence of small changes in mortality against side small and that possible harms needed to be considered. Instead, ffects of screening and treatment. Because of the impact of screen- USPSTF recommended that physicians discuss the risks and benefits ing biases, only a change in overall mortality in the screened popula- eening with the women and to proceed according to the tion is considered evidence of an effective screening program. The benefit preferences. This change led to a significant media backlash debate about changes in the U.S. Preventive Services Task Force Many people claimed the decision amounted to"care rationing, and demonstrate that that the USPSTF had overstepped its mandate by weighing mortality few issues in preventive medicine have er to polarize the benefits against anxiety. The Task Force argued that the evidence and health care prof ort a"one size fits all" recommendation and that their guidelines empowered patients and their physicians to make rational Breast Cancer cisions based on evidence and more respectful of individual an io oe resp rematrurelities best cd ne. mnatormuonatemy, truly lead to a saved life; the majority are false-positive findings or lead = As of 2012, the rating is a"B" for women age 50 to 74( nded )and a"C for women 40 to 49, indicating that USPSTF the decision to screen should be individualized, and the net necessary diagnosis and treatment of lesions such as ductal carci is likely small. noma in situ(DCIS), which is not harmful to the majority of women Most women would not have known they had these DCIS lesions Prostate Cancer had it not been for the screening mammography. Women with DCIS re at increased risk for a subsequent diagnosis of invasive breast Prostate cancer affects men in a broad age range and has a wide cancer. Unfortunately, we cannot predict which women with DCIS whereas others are slow-growing and indolent. False-positive will ultimately go on to have invasive breast cancer. Thus, women results of prostate-specific antigen( PSA) testing are common ho are diagnosed with DCIS after a screenIng mammography often undergo breast surgery, chemotherapy, and radiation treatment that and often lead to other unnecessary invasive testing (e. g, biopsy can be costly and traumatic. Similarly, many women whose cancers This testing can then lead to diagnosis(often without a reliable way are detected by mammography still die of their disease. If mammo to distinguish between indolent and aggressive disease), treatment (e.g,surgery, radiation, and/or chemotherapy), and serious harm, mortality in populations screened should decrease. This hypothesis including erectile dysfunction, bladder and bowel incontinence, and death, to manage a disease that might otherwise have never been problematic(most men die with prostate cancer, not of prostate As of 2011, the strongest evidence shows that any difference in To date, the evidence that prostate verall mortality between populations exposed to screenings and cancer screening decreases all-cause or prostate cancer-specific those not screened is small: for every 2000 women invited for screen mortality. If there is any benefit, it likely accrues over more than 10 g throughout 10 years, one will have her life prolonged; 10 healthy years. Therefore, USPSTF advised in 2012 against routine screening omen who would not have been diagnosed if there had not will experience important psychological distress for many months Both these controversies illustrate the need of personalizing screen- because of false-positive findings tate cancer should be based on the patients risk preferences and In 2009, USPSTF changed its screening recommendations regarding willingness to have false-positive test results and invasive follow-up breast cancer for women age 40 to 49, Previously recommending testing. Many decision aids have been developed to help individua routine screening in this population, the Task Force now argued that make informed decisions They may delay medical visits that they might otherwise conducted. An RCT is needed to reduce the potential for have made promptly. False-negative results also may falsely bias In cancer an association between screening and longer reassure clinicians False-negative results can be detrimental survival does not prove a cause-and-effect relationship to the health of the people whose results were in error, and because of possible problems such as selection bias, lead test results delay the diagnosis in people who have an infec tious disease, such as tuberculosis, the screening tests can be Selection bias may affect a screening program in different dangerous to the health of others as well directions, all of which may make it difficult to generalize Overdiagnosis is another potential harm of scree ening findings to the general population. On one hand, individuals programs. For example, screening mammography may lead may want to participate because they have a family history to a diagnosis of a preinvasive lesion that is not invasive of the disease or are otherwise aware that they are at higher breast cancer(see Box 16-1). Actions taken in response to risk of contracting the disease. In this case the screening uch findings, including surgery, may result in a scenario program would find more cases than expected in the general where the ostensible " cure"is in fact worse than the disease. population, exaggerating the apparent utility of screening On the other hand. individuals who are more"health con- E. Bias in Screening Programs scious"may preferentially seek out screening program It is not easy to establish the value of a community screening Lead-time bias occurs when screen ling detects disease