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2. SCREENING OVERVIEW 12 2. SCREENING OVERVIEW The committee was asked to address the screening of the populations of uranium miners, millers and ore transporters, and downwinders and onsite nuclear-test participants for a broad set of malignant and nonmalignant diseases compensable under RECA. However, not all the compensable diseases are considered to be radiogenic. Although the objective of the screening process used by the grantees should be consistent with accepted rationales for screening populations or patients, many persons in the RECA-covered populations do not have clinical evidence of disease. The HRSA program addresses the identification and compensation of people who have developed diseases covered under RECA. The dual goals of the program may, and at times do appear to be, in conflict. The program assumes that screening exposed people will provide health benefits to them. However, such benefits have not been established on the basis of evidence; indeed, the committee has heard testimony that some of the screening anticipated by the legislation may be harmful. The decision to screen for purely medical reasons rests on a hierarchy of assumptions that â¢ A disease exists in the population, and effective treatment for or prevention of preclinical or early-stage disease is available. â¢ An accurate, practical screening test is available. â¢ Early detection improves clinical outcomes (such as survival or quality of life) of the disease. â¢ An effective treatment for, or a means of prevention of, a preclinical or early-stage disease is available. â¢ The benefits of screening exceed its harms. â¢ The cost of a screening program (including its induced costs) justifies the use of resources. â¢ An existing health-care system has the resources to provide referral services that address follow-up (further evaluation and continuing care) of patients identified through the screening program, including the noncompensable diseases coincidentally identified. It remains difficult to establish that screening programs in actual practice meet those criteria, in part because of confounders such as lead-time and length bias. Furthermore, any program may be considerably less effective in practice than in theory. Effectiveness in practice depends on a long chain of causal reasoning that is subject to âfailureâ at many of its steps.
2. SCREENING OVERVIEW 13 In the context of the screening program anticipated by HRSA, an additional set of issues might be considered: â¢ Most prior analyses of medical screening have considered programs that addressed a single disease; the HRSA program screens for a multitude of diseases simultaneously. (Indeed, multiphasic screening programs were popular about 2 decades ago (for example, for executives) until it became clear that the problem of false positive, and red herrings limited their utility). â¢ Screening for medically marginal indications compete in the same resource pool as screening for more- accepted indications (such as diabetes, hypertension, hyperlipidemia, and colon cancer), and the screening and follow-up of people in the HRSA program may make such more-accepted approaches to preventive care unavailable to this population. â¢ Compensation to some of the people subjected to a potentially harmful screening program may partially offset the risks and might be a consideration for some people in deciding whether to participate in the HRSA program. Although the committee heard testimony that the issues of medical benefits or harms and of compensation should be kept separate, the issues must come together for people in the RECA populations to make an informed decision about participation in the program. The committee believes that people eligible for a screening program should be well informed about the potential harms and the benefits of such screening. Most screening programs address a single disease, a disease for which early detection makes a difference and for which a highly specific, typically binary test is available (for example, leading to a positive or negative result). That is not the case for most of the diseases covered under RECA. Several independent guideline-producing agencies have not recommended a number of the RECA targeted diseases for screening. In the case of lung cancer, this can be attributed to the lack of demonstrated medical benefit from early detection and the lack of a practical, highly specific test. The same is true, for example, for thyroid cancer. Because screening programs such as those being proposed to HRSA involve testing for diseases with low prevalence, false-positive rates will be high and will be accompanied by increased risks and costs associated with further testing. Bayesâ rule shows that the probability of disease among patients with a positive (screening) test (the positive predictive value) depends most strongly on the testâs specificity and the probability of disease in the population to be screened. If both are relatively low (likely the case in the HRSA program), the positive predictive value will be low, and the majority of positively labeled people will, in fact, be false positives. The false-positive problem is exacerbated when one screens for several diseases or when the test under