Assessment of the Scientific Information for the Radiation Exposure Screening and Education Program (2005) / Chapter Skim
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9 Medical Screening
9 Medical Screening
Pages 219-256
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1515] July 10, 2000 Radiation Exposure Compensation Act Amendments of 2000 106 PL 245; 114 Stat.
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(A) of the Radiation Exposure Compensation Act (42 U.S.C.
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This distinction is not traditional but is required because RESEP specifies screening for some diseases not traditionally recommended for medical screening to improve health outcomes. Because a term is required to describe this RESEP concept, we coin the term compensational screening.
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222 RADIATION EXPOSURE SCREENING AND EDUCATION PROGRAM TABLE 9.1 Screening Protocols in RESEP Compensable Nonmalignant Radiogenic Compensable Malignant Screening Protocols Diseases Radiogenic Diseases Medical and Must include date of exposure, Must include date of exposure, occupational place, duration of employment, place, duration of employment; history and tobacco use special attention to symptoms of and risk factors for primary cancers or other diseases covered by RECA; should also include tobacco, alcohol, and caffeine use Physical examination Emphasis on pulmonary, Complete examination to cardiovascular, and renal include all cancers covered by systems RECA Chest radiography Standard posterior-anterior As indicated by physician view chest radiograph for presence of radiologic fibrosis, silicosis, or pneumoconiosis Pulmonary-function As needed, can include See physical examination testing spirometry, lung volumes, arterial blood gases, and DLCOa Routine testing Other routine laboratory work Routine laboratory work as and electrocardiography as indicated by physician required Other Program Requirements Included in Screening and Early Detection Followup Patient contact via telephone; See case management below report results to patient, primary care physician, or both; periodic re-evaluation Case management Not required Extensive followup to ensure that care was received; documented monitoring of patient progress; all operative, consultative, procedural, and pathology reports and physician, hospital, and health care facility discharge summaries maintained aDLCO, the diffusing capacity of the lung for carbon monoxide (CO) , i.e., measurement of carbon monoxide transfer from inspired gas to pulmonary capillary blood (American Thoracic Society, 1995)
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. Positive results from screening tests are usually not conclusive, so confirmatory tests are needed before a diagnosis is established; if such a diagnosis is made, then followup, referral, and treatment would typically be expected to ensue.
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Third, particularly for compensational purposes, medical screening tests are appropriate only after the individuals are fully informed of the risks that these tests pose (see Chapter 8)
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Of particular importance are sensitivity, specificity, and positive and negative predictive values. Increasingly, policy makers, clinicians, and others concerned with screening issues are called on to deal with odds ratios, likelihood ratios, and receiver operating characteristic (ROC)
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. Because screening tests commonly have sensitivity below 100%, false-negative results will also occur, but these errors may be far less problematic in the screening setting (see discussion later in this chapter)
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Appendix E presents current information on cancer screening tests of interest to this committee; some are for RECA-designated diagnoses and others for nonradiogenic cancers; as a more complete context for considering medical screening in primary care, we also present there a fuller account of the types of screening tests the USPSTF recommends or strongly recommends for general populations other than RECA populations. As seen in Appendix E, relatively few screening tests for cancer have been recommended for widespread use.
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, and surgical mortality. Although most screening tests are themselves of low risk and noninvasive, some screening tests expose individuals to ionizing radiation.
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Consider a screening program for a single cancer for which early detection provides a huge therapeutic benefit of 10 years of added life expectancy, as illustrated in Table 9.3. Assume that a screening test has a high sensitivity of 90% and that the prevalence of disease in the population to be screened is 2 cases per 1,000 individuals.
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This view reflects the ethical principles introduced in Chapter 8 and the tenets of shared decision-making taken up later in this chapter. Similar issues arise in medical screening for most RECA-compensable diseases
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. EPIDEMIOLOGIC, STATISTICAL, AND CLINICAL ISSUES OF SCREENING TESTS The complexities of interpreting the risks posed by and the results of screening tests (whether in general or for RESEP)
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What Is a Positive Screening Test? Throughout this chapter and this report, we use the terms positive and abnormal to describe a test result.
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However, having a simple criterion of positivity allows clinicians to interpret the meaning of the result more readily in the context of a particular patient who may have a particular pretest likelihood of disease, which often will be based on clinical presentation, history, demographics, and even physical examination or other known test results. With a criterion of positivity, the performance of a test can be described on the basis of two characteristics: sensitivity and specificity (Figure 9.2)
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curve is particularly useful. The Receiver Operator Characteristic Curve for a Test A critical question in interpreting screening tests is how and where to establish a criterion of positivity -- that is, the cutoff (cutpoint)
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More typically, clinicians select an optimal cutoff, thereby establishing the test's operating characteristics, and only then do patients and clinicians choose whether to perform the test. Typically, distributions of screening tests overlap.
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× (BurdenFalseNegative) The burden of a false-positive result is defined as the degree to which an individual without disease but with a falsely positive test result is less well off (on some outcome scale)
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Thus, as one considers medical screening tests for the RESEP populations, one should consider the prevalence of disease in each case. Doing so implies a program that is administratively far more complex than RESEP (or HRSA grantees)
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These are complex and important relationships. Early in this chapter, we used the terms strict and lax to describe criteria for defining a positive test.
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In Figure 9.4B, these three populations have been merged into two groups -- patients with disease and patients with no disease -- by defining disease to be only severe disease. The nodisease category now includes some patients with mild disease, and patients in this category are more likely to have a positive test result than are patients in the mild severe disease disease Result Test Result estT of Probability no disease FIGURE 9.4A Probability of test result in three populations defined by presence and severity of disease.
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compared to just looking at the test in patients who have no disease at all. In contrast, test sensitivity will increase compared to a mix of patients with mild and severe disease because all patients now classified as having disease will have severe disease and therefore be more likely to have a higher test result.
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The Meaning of a Positive Test Sensitivity, specificity, and ROC curves apply to two populations: individuals without disease and individuals with disease. In contrast, the task that the clinician interpreting a screening test faces deals with an individual who is not known to be a member of either population.
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In the simple case of a test that is either positive or negative and a disease that is either present or absent, the revised or posterior (posttest) probability (also known as the positive predictive value)
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The Conundrum of the False-Positive Cascade RESEP proposes screening for 20 malignant conditions in downwinders and onsite participants, seven malignant and nonmalignant conditions in uranium millers and ore transporters, and six other conditions in miners. The specificity of each of the proposed screening tests for these separate conditions is likely to be well below 95%.
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90% 0 0.9000 0.8100 0.7290 0.6561 0.5905 0.5314 0.4783 0.4305 0.3874 0.3487 0.3138 0.2824 0.2542 0.2288 0.2059 0.1853 0.1668 0.1501 0.1351 0.1216 Effect the positive Results in no Two Cascade: or Equals having 2 0.0025 0.0071 0.0135 0.0214 0.0305 0.0406 0.0515 0.0629 0.0746 0.0867 0.0988 0.1109 0.1229 0.1348 0.1463 0.1575 0.1683 0.1787 0.1887 examples a of to One, None, 1 0.0500 0.0950 0.1354 0.1715 0.2036 0.2321 0.2573 0.2793 0.2985 0.3151 0.3293 0.3413 0.3512 0.3593 0.3658 0.3706 0.3741 0.3763 0.3774 0.3774 Specificity probability correspond of False-Positive That the is The Level 95% 0 0.9500 0.9025 0.8574 0.8145 0.7738 0.7351 0.6983 0.6634 0.6302 0.5987 0.5688 0.5404 0.5133 0.4877 0.4633 0.4401 0.4181 0.3972 0.3774 0.3585 boldface = in Probability 9.4 N specificity Items joint Tests TABLE The Number of 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 a NOTE:
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Screening Trial (Lafata et al., 2004) , in which the joint specificity of four screening tests was 49.11% among men and 64.0% among women.
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In that case, the two results would be very dependent, and one would not TABLE 9.5 Interpretation of Two Diagnostic Tests Individual Joint Parameter Test 1 Test 2 AND OR Sensitivity 70% 80% 56% 94% Specificity 90% 95% 99.5% 85.5% Positive Predictive Value Disease Prevalence 1% 6.6% 13.8% 52.8% 6.1% Disease Prevalence 20% 58.6% 76.2% 95.7% 56.5%
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Using the same example as above, the joint sensitivity will be 94% and the joint specificity will be 85.5%. In a screening setting with low prevalence, a lower specificity will probably produce a lower positive predictive value.
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These factors make the mathematics a bit more complicated because one needs to think in terms of conditional probabilities (for example, the conditional probability of a positive test given the presence of disease 2)
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That threshold may vary from test to test for a specific disease (see the discussion above of lead time bias and the inherent biases of using more sensitive screening tests)
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Third, as the exposed population ages and comorbidities develop, the medical benefit of early detection in improving life expectancy wanes. Thus, for downwinders and onsite participants, little rationale can be advanced for expanding medical screening recommendations in the RECA populations beyond contemporary recommendations for the general population (as in Appendix E)
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The committee finds insufficient supporting evidence to support additional medical screening or medical case-finding in the RECA populations beyond the level and type of screening advised for general populations and persons with occupational exposures similar to those of in miners in general. Specifically the committee recommends that the Health Resources and Services Administration base RESEP medical screening efforts in asymptomatic individuals on robust scientific evidence that such screening improves health outcomes and that its benefits outweigh its risks.
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The committee encourages Congress to expand financial support for rigorous studies of diagnostic and screening tests, including cost-effectiveness analyses. As documented elsewhere in this report, the six current HRSA grantees operate screening programs with quite different orientations.
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The sensitivity, specificity, and positive and negative predictive values (or reliability and validity) of a variety of screening tests may well differ in those populations from the values in populations of either average or low risk.
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. This evolution in clinical-practice guidelines since that time for both primary and specialty or referral care, may have implications for both RECA populations and the RESEP program.
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rapid, simple, low-cost screening tests for depression are available and have been validated (Pignone et al., 2002)
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Finally, we have offered several recommendations to reduce potential harms and mistakes from the use of multiple screening tests among individuals for whom the medical benefits cannot outweigh the harms and the likelihood of compensation may be low. Some recommendations are directed at agents that would need to amend RECA (or RESEP)
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