DoctorFinder | Join/Renew | MyAMA | Site Map | Contact Us

NOTE:  This report of the Council on Scientific Affairs (CSA), represents the medical/scientific literature on this subject as of June 2003.  Written in response to  Resolutions 508 (I-01) and 509 (A-02), it was presented as CSA Report 10 at the 2003 AMA Annual Meeting.

Methods
Established Screening Criteria
Variables That Confound Assessment of Screening Tests
Commercialized Medical Screening
Coronary Artery Calcium Screening
Spiral Helical (Low-Dose) CT (LDCT) Screening for Lung Cancer
CT Scanning for Colon Cancer
Whole Body Scans
Conclusion and Comment
Recommendations (Adopted AMA Policy and DIrectives)
References

The proliferation and direct marketing of screening tests that lack a credible evidence base, or that misrepresent their true risks and benefits, raise a number of scientific, clinical, and ethical concerns. Although it can be argued that patients (consumers) have the right to purchase these kinds of "health care" scans, the profession of medicine carries certain responsibilities that are relevant to these issues. The American Medical Association (AMA) has long-standing policy that any preventive services should be supported by evidence-based data to demonstrate improved outcome or quality of life and the cost-effectiveness of the service (Policy H-425.997, Preventive Services, AMA Policy Database).

A September 2002 statement issued by the American College of Radiology (ACR) stated that "to date, there is no evidence that total body computed tomography (CT) screening is cost-effective or effective in prolonging life. In addition, the ACR is concerned that this procedure will lead to the discovery of numerous findings that will not ultimately affect patient’s health but will result in unnecessary follow-up examinations and treatment and significant wasted expense."1 The CSA agrees with this statement and, due to the lack of published sensitivity and specificity data on this procedure, will not further examine it at this time. This report also does not examine the emergence of positron emission tomography scans that certain facilities have recently begun to promote. This report will focus on the use of electron beam computed tomography for determining coronary calcification and the use of CT for lung and colon cancer screening. However, a comprehensive review of these technologies is beyond the scope of this report.

Methods

Literature searches were conducted in the MEDLINE and Nexis databases for English-language articles published between 1990 and March 2003 using the search terms screening, mass screening, and tomography, x-ray computed or radiography, as well as the text terms electron beam computed tomography, or virtual colonoscopy, in combination with calcium, coronary angiography, coronary arteriosclerosis, coronary disease, lung, lung neoplasms, thoracic, adenocarcinoma, colon, colonoscopy, colorectal or colonic neoplasms, colonography, and colonic polyps. A total of 812 citations were identified; 272 were retrieved for analysis. Additional references were culled from the bibliographies of these references.

Established Screening Criteria

Screening constitutes the use of laboratory tests, physical examination, or imaging modalities performed on asymptomatic patients with the intent of identifying subclinical disease. As such, screening differs from clinical investigation, in which tests are ordered after disease is suspected. The AMA defines screening as health care services or products provided to an individual without apparent signs or symptoms of an illness, injury, or disease for the purpose of identifying or excluding an undiagnosed illness, disease, or condition (AMA Policy H-320.953).

A screening test is the initial action in a screening program, which also includes follow-up tests to confirm the initial test results (eg, biopsy, angiography) and treatment given for abnormal findings (eg, surgery, radiation, chemotherapy, pharmacotherapy). Early detection represents discovery of a condition or disease before obvious signs or symptoms have appeared. Screening can be further subdivided into mass screening or individualized screening. The former is conducted with little regard for the risk profile of the individual patient. Most physicians are involved in the latter, which consists of recommending screening tests in the context of an ongoing patient-physician relationship. The sensitivity and specificity of a particular test help establish its effectiveness. Sensitivity equals the proportion of the disease population who have a positive test (true-positive rate). The specificity of a test equals the proportion of healthy patients who have a negative test (true-negative rate). Patients and clinicians are often more interested in the positive predictive value of a test, which equals the proportion of patients with a positive test result who actually have the disease.

For a screening test to be considered effective, certain criteria should be fulfilled, including the following:

  • The disease must constitute a significant public health problem (common, with significant morbidity and mortality).
  • The disease or condition should have a readily available and acceptable treatment, and the potential for cure must be greater among screen-detected patients.
  • The screening test must have appropriate sensitivity, specificity, and positive predictive value (capable of detecting a sufficiently high proportion of [disease] in the detectable preclinical phase).
  • The screening test should be acceptable (and safe) to the patient and society.
  • There must be demonstrable improved health outcomes related to screening.
  • The screening procedure should have a reasonable cost.
  • Adequate resources and health services should be available to accomplish the screening and to provide the necessary intervention triggered by a positive test result.

Additionally, when a new screening test becomes available, it should offer significant advantages in terms of information obtained, cost, or safety over other alternative tests when more than one test is available to screen for the same disease. Back to Top

Variables That Confound Assessment of Screening Tests

Several biases are inherent in the conduct of screening tests that can have an impact on apparent survival measures, thus affecting valid assessment of screening test effectiveness. In particular, lead time bias makes the assessment of mortality improvements difficult. Early detection of cancer creates a backward shift in the starting point for measuring survival (earlier diagnosis), which may artificially increase incidence and lengthen survival.

Screen-detected incidental cancers represent length bias. Individuals with more slowly progressive disease (eg, prostate cancer) will tend to be detected. Length bias increases the incidence of early-stage disease and lengthens apparent survival, but has no effect on mortality rates or advanced-stage disease.

People who agree to be screened are a self-selected group who may be more aware of the disease in question and more health conscious. Selection bias can occur whenever the group actually screened differs from the potential population of individuals to be screened. This bias also can cause apparent increases in survival of individuals with screen-detected conditions. Overdiagnosis bias occurs when a screen-detected abnormality is labeled as the "disease" when in fact this abnormality would never have been clinically diagnosed in the absence of screen detection. This may be particularly relevant for lung cancer (or whole body) screening with CT scans.

Because of these biases, case survival cannot be used to assess the effect of screening on mortality. In fact, 5-year survival figures are unrelated to cancer mortality on a population basis.2 Rather, population mortality from the disease over a follow-up period beginning with randomization should be used. Also, one generally cannot make valid comparisons by comparing people screened with those who were unscreened in the past. The only way to determine the degree of benefit without bias is by comparing people offered screening with a group of truly comparable people who are not offered screening.

Some common methodologies used in observational epidemiology, particularly case-control and cohort studies, are sometimes used to evaluate screening. Valid application of these approaches requires that screening has been in place in a community for a sufficient length of time for a benefit to be detectable if it does occur. Case-control studies have limitations because it can be difficult to differentiate a screening test from a diagnostic test for cancer, and this imprecision in classification can have a major impact on the results of such studies. Back to Top

Commercialized Medical Screening

Community-based screening programs for blood pressure, cholesterol, other serum chemistries, and certain cancer screening tests (eg, mammography, prostate-specific antigen) have been offered for many years. More recently, the development of high-technology imaging tests such as electron-beam computed tomography (EBCT) for the detection of coronary artery calcium, spiral CT scan for lung cancer, CT colonography ("virtual colonoscopy"), and even "whole body scans" have been marketed directly to the public. These new imaging techniques are offered on the premise that they identify the presence of subclinical disease, improve chances of survival, or are more convenient.

Although their relative risks and benefits are not established, ensuing public and professional interest has led to the early adoption and promotion of these scans. Consequently, the emergence of for-profit imaging centers and direct-to-consumer advertising has led to significant numbers of self-referred patients with abnormal test results seeking treatment advice from their physicians.

Coronary Artery Calcium Screening

The most common commercially available test to evaluate coronary artery calcification is EBCT; multidetector CT protocols and others also are being devloped. EBCT uses a stationary source-detector combination and a rotating electron beam to produce serial and contiguous thin-section, 100-millisecond scans at end-diastole in synchrony with the cardiac cycle. Scans can be completed in one or two short breath holds. Calcium is readily apparent as high-density deposits adjacent to lower density soft tissue and fat. Standardized methods for scanning, identification, and quantification of coronary artery calcification (CAC) have been established.3 EBCT is being directly marketed for the purpose of screening and assessing asymptomatic patients. It is also being used clinically to assess CAC in patients of intermediate to high risk of developing cardiovascular disease; in symptomatic individuals at low to intermediate risk of coronary events to stratify patients for more aggressive primary prevention; and in patients with known coronary artery disease (CAD) to assess progression or regression of the total plaque burden. Most EBCT centers rely on self-referred patients for the majority of their volume of procedures.

Coronary plaque burden has been established as a good predictor of future coronary events.4,5 Although the amount of CAC detected by EBCT represents a small percentage of the total plaque burden (~20%), the extent of CAC (total calcium score) correlates with the severity of atherosclerosis. EBCT is less sensitive for detecting lipid-laden, vulnerable plaque, the rupture of which is often associated with acute coronary syndromes.6-12 Additionally, some high-grade stenoses may lack detectable levels of calcium. Nevertheless, because of the above relationships, CAC is believed to have some predictive power for future coronary events.

Currently, clinicians rely on traditional models of risk-factor analysis to predict coronary outcomes, make therapeutic decisions, and attempt to change patients’ behavior. Risk stratification based on the Framingham model has limited sensitivity and specificity for identifying individuals who will suffer an acute catastrophic coronary event. A significant number of events that occur in asymptomatic patients at low to intermediate risk are believed to be caused in part by plaque rupture (or erosion) of mild, nonobstructive arterial stenoses, which may not be calcified.13,14 Plaque characteristics unrelated to the degree of stenosis, such as lipid content and plaque wall thickness, may be better predictors of rupture than the degree of obstruction. Thus, a question of considerable importance for primary prevention is how the information attained through CAC determinations can be used in risk assessment and in the selection of patients for more intensive risk reduction therapy.

Clinical Trials on EBCT. Several prospective studies have been conducted on the use of EBCT for diagnosis of CAD and/or risk prediction. A meta-analysis of 16 EBCT studies involving patients without a prior history of coronary disease who presented for diagnostic catheterization found that the use of EBCT was associated with an 80% sensitivity, 40% specificity, and 59% positive predictive value for the presence of CAD.7 The case definition of CAD was variable, although stenosis ≥50% was used in the majority of these studies. Significant CAD was detected in 60% of patients, and significant CAC was present in 68%. In this analysis, the sensitivity of EBCT was similar to that of other noninvasive tests for ischemic heart disease, but had a higher false-positive rate, particularly in the elderly.7 Another meta-analysis that included only studies where CAD was defined as ≥50% stenosis found somewhat higher values of 92% for sensitivity and 51% for the diagnostic specificity of EBCT (compared with catheterization).15 Thus, data are consistent with the "calcium score" being viewed as a surrogate for overall atherosclerotic plaque burden, and for providing ranges of variable sensitivity and specificity of luminal narrowing for at least one vessel without identifying specific lesions or sites.16,17

A more relevant question for the use of EBCT as a commercialized screening test is its ability to predict the risk of future coronary events, either independently or incrementally in conjunction with traditional validated risk factors. Several studies attempted to evaluate whether the CAC score can independently predict risk in asymptomatic patients (who nevertheless have certain risk factors) (see Table).18-21

Results of these studies indicate that EBCT calcium scores have some predictive value, although the studies to date are weakened by selection and treatment biases.22 A meta-analysis found a pooled risk ratio for death or nonfatal myocardial infarction of 4.2 (over 42 months) when the CAC was above the median value, although the validity of this meta-analysis has been questioned.23,24 Asymptomatic patients with calcium scores below sex- and age-specific means are less likely to have obstructive atherosclerosis than patients with greater than average scores, and the negative predictive value of EBCT is high (92% to 98%). However, the relationship of EBCT calcium scores to traditional risk factors and whether they offer incremental value is not established.8,21 In one recent study involving an age-homogenous male sample (aged 39 to 45 years) with a low predicted risk of coronary events, the prevalence of CAC was 17.6%. Calcium scores were independently associated with low-density lipoprotein (LDL) concentrations and had only a weak relationship with the Framingham risk index.25

Comment. Self-referral for EBCT is based on the premise that conventional cardiovascular risk factors inadequately quantify risk. Despite promising results, questions remain about the current value of this technology in asymptomatic patients, because most of the research data come from symptomatic or high-risk, older, and primarily self-referred populations. Evaluations have involved mostly comparisons with angiographic disease determination based on variable degrees of obstruction. It remains to be established how information obtained through EBCT can be used in risk assessment and in the selection of patients for more intensive primary preventive therapy. Additionally, the extent to which CAC predicts the development of coronary events independent of standard risk factors (eg, cigarette smoking, hypertension, elevated LDL, family history of premature coronary heart disease [CHD], etc) has not been resolved. Furthermore, the use of EBCT must be evaluated in comparison with alternative noninvasive tests (eg, nuclear stress test; stress echocardiogram), both of which allow for functional assessment of the coronary arteries (in contrast to EBCT) and are frequently used to clarify the significance of an abnormal EBCT before deciding if the patient requires angiography.

Several studies are under way in heterogeneous patient sets to confirm the utility of EBCT. A large registry has been established by the Society for Atherosclerosis Imaging and a large observational epidemiological study sponsored by the National Heart, Lung and Blood Institute is investigating CAC, detected by EBCT, as a predictor of CHD mortality and morbidity, stroke, and all-cause mortality. The National Institutes of Health Multiethnic Study of Atherosclerosis will assess the long-term outcome of 6,500 asymptomatic individuals undergoing EBCT, as well as other imaging and nonimaging tests.26 This trial should provide important information on EBCT and other measurements that may detect subclinical coronary artery disease. The Prospective Army Coronary Calcium Study includes a study arm to establish the relationship between CAC and cardiovascular events in a "low risk" military population.27 As part of the Dallas Heart Disease Prevention Project, approximately 3,000 randomly selected subjects aged 30 to 60 years will undergo EBCT.

The American College of Cardiology/American Heart Association Expert Consensus Document on Electron-Beam Computed Tomography (EBCT) for the Diagnosis and Prognosis of Coronary Artery Disease15 states that the "published literature does not clearly define which asymptomatic people require or will benefit from EBCT," and that "EBCT screening should not be made available to the general public without a physician’s request." Until clinical trial data become available, evidence-based guidelines for the prevention of cardiovascular events based on EBCT results are lacking, particularly in the case of asymptomatic patients. Advice given in regard to coronary risk stratification or therapy modifications should be based on well-designed epidemiological studies and prospective randomized clinical trials.

Spiral Helical (Low-Dose) Computerized Tomography (LDCT) Scanning for Lung Cancer

Lung cancer is the number one cause of death in the United States for both adult men and women, claiming approximately 150,000 lives annually. Most patients who are diagnosed with lung cancer have advanced stage, symptomatic disease. In the United States, only 20% of diagnosed lung cancers are in stage 1.28

Previously, 4 large randomized controlled trials enrolling approximately 37,000 high-risk male smokers more than 45 years of age evaluated the impact of regular chest X-ray (CXR) on lung cancer mortality.29-34 Investigators in each trial found an increased incidence of earlier stage lung cancers, more resectable cancers, and improved 5-year survival rates in the screened groups, but no trial found a statistically significant decrease in disease-specific (lung cancer) mortality.35 The survival/mortality differential in the Mayo study has been attributed to length and overdiagnosis bias.36

Because of contamination of the control group (a large percentage of subjects had CXR) and other methodological concerns, disagreement persists on the conclusions of the Mayo study, and whether it truly invalidates the potential benefit of annual CXR screening for lung cancer.37 However, based on the results of these trials, the general consensus has been that screening for lung cancer with chest X-ray ± sputum cytology has no beneficial effect on mortality. Nevertheless, in another attempt to definitively evaluate the mortality benefit of CXR screening for lung cancer, its use as a screening tool is currently being studied in the Prostate, Lung, Colorectal and Ovarian Cancer Screening Trial.38

LDCT scanning is very sensitive (compared with CXR), and is capable of routinely detecting nodules 2 to 3 mm in diameter. Three-dimensional reconstruction creates images that can be assessed sequentially to monitor for growth. The rationale for LDCT as an improved early detection technology is therefore based on its ability to detect smaller nodules, allowing for surgical resection of more patients who have stage 1 disease. In Japan, the Anti-Lung Cancer Association added LDCT screening to CXR screening in 1993. CT screening using mobile units has been offered in certain regions of Japan, and to individuals enrolled in certain insurance groups.39-41 A nonrandomized historical comparison of CXR + sputum cytology to CXR ± sputum cytology + LDCT found that use of CT scans nearly doubled the percentage of stage 1A tumors represented in the diagnostic cohort, and appeared to markedly improve 5-year survival (48% to 82%).39 Whether the latter represents a true mortality benefit may be clouded by lead time and other biases.

Clinical Trials of LDCT Screening. LDCT has been studied in several observational screening studies in high-risk patients.39,40,42-48 To date, primarily prevalence data from these trials have been published. Relative to CXR, LDCT enhances the detection of small noncalcified modules and of lung cancer at an earlier stage.49 The rate of lung cancer diagnosis obtained from baseline screens was 0.4% to 2.7%, much higher than normal baseline rates of lung cancer diagnosis; 77% to 100% of these malignancies were stage 1 disease. However, all of these studies had a high rate of false-positive results, with abnormal nodules reported in 12% to 51% of screened patients. The number of suspicious lesions observed in an asymptomatic general population would be expected to be much smaller. In one study of subjects who responded to offers of screening (40% nonsmokers), suspicious nodules were detected in 5.1% of subjects, 8% of whom were confirmed surgically to have lung cancer (0.4% of original pool).47

Because LDCT screening advances the stage at which lung cancer is typically diagnosed, and unresected stage 1 disease has such a dismal 5-year survival rate, screening for lung cancer by LDCT would seem to be an effective means to prevent deaths from lung cancer.48 However, concerns remain that LDCT leads to overdiagnosis and its widespread application may result in aggregate harm to screened individuals because the rate of benign nodule detection is high. The apparent false-positive to true-positive ratio in screening studies of high-risk patients has ranged from 10 to 30.4,6,49 In one recent study, 50% of patients referred for biopsy had negative results. Additionally, there are currently no data to show that a 5-mm diameter lung mass is associated with substantially better prognosis than a 10-mm mass.50 Various protocols have been used for following up indeterminate nodules in an effort to reduce unnecessary invasive procedures.41,46,49-51 Use of serial CT scans and 3-dimensional reconstruction appears to lessen the number of invasive procedures performed on individuals who have an abnormality. 52

A large New York-based LDCT study enrolling 10,000 current or former smokers and a National Cancer Institute (NCI) lung screening study will evaluate the risks and benefits of LDCT. The NCI study is enrolling 50,000 individuals aged 55 to 74 years with a smoking history of at least 30 pack-years. They will be randomized to annual screening with LDCT or CXR for 3 years and followed up through 2009 (unless an obvious early disease-specific mortality benefit is observed).

Comment. The American College of Chest Physicians (ACCP) recently commissioned the development of evidence-based guidelines for lung cancer prevention, diagnosis, and treatment. The ACCP recommends "against the use of a single LDCT or serial LDCTs to screen for the presence of lung cancer." At-risk individuals who express an interest in undergoing LDCT screening should be made aware of several ongoing high quality clinical studies of this technology."53 The American College of Radiology statement54 on LDCT expresses "concern about the broad dissemination of lung screening outside of experienced, multispecialty settings and prior to the validation of this new technology and encourages professional organizations to promote informed decision-making for patients about possible benefits, risks, and limitations of testing for early lung cancer. Individuals interested in early detection (screening) should be encouraged to participate in trials." Similarly, the Society of Thoracic Radiology "does not recommend mass screening for lung cancer at this time, but strongly encourages appropriate subjects to participate in trials so that the true effectiveness of lung cancer screening with LDCT can be determined at the earliest possible time."55 Until more data are available and the NCI randomized trial is completed, "physicians, patients, and policy makers should be conservative about accepting this new, as yet not fully tested, and relatively expensive strategy of using helical CT scanning for lung cancer."56

The appropriate goal of any population-based screening program is to protect the public’s health, while targeting the test individuals most likely to benefit. The argument over routine use of LDCT reflects a divide over what evidence is required and how it should be obtained before an emerging early cancer detection technology is broadly adopted. From a public health perspective, smoking cessation must remain the first and foremost priority in reducing the burden of lung cancer in the population. LDCT may prove to be a very important tool for early detection of lung cancer, but at this time, only prevalence-screening data and preliminary survival data in observational cohorts are available. It remains to be established whether LDCT screening for lung cancer will truly reduce mortality in safe, cost-effective manner. Studies like the New York-based LDCT study and the NCI multicenter trial will likely provide this vital information.

Computerized Tomography Scanning for Colon Cancer

Colorectal cancer is the second most common cause of death due to cancer in the United States. Most colon cancers arise from pre-existing benign adenomatous polyps. Detection and removal significantly decreases the subsequent development of colon cancer.57 Conventional colonoscopy is considered the most effective modality for the prompt detection of colorectal cancer. Colonoscopy has a sensitivity of 95% for detection of colorectal cancer in clinical practice, but complete examination of the colon is not possible in 5% to 15% of all patients, and a missed lesion rate of 6% has been reported for the detection of polyploid lesions measuring more than 1 cm in diameter and 13% for lesions 6 to 9 mm in diameter.58,59

CT colonography (CTC), also known by the marketing term "virtual colonoscopy," was first introduced in 1994 and has evolved rapidly. Several recent reviews are available.60-63 CTC involves thin-section helical computed tomography of a clean, air-distended colon (using a rectal enema tube), to generate high-resolution, 2-dimensional axial images. Application of advanced graphical software to the volumetrically acquired helical CT data generates 3-dimensional images of the colon off-line. Performance over the last decade has improved with the availability of ultrafast helical CT scanners (multidetector CT) and advances in computer software for image reconstruction. However, there appears to be a steep learning curve to establish competency in correct interpretation.64

Compared with conventional colonoscopy, CTC has lower risk; carries no need for sedation, analgesia, or recovery time; and can eliminate "blind spots" proximal to colonic folds. CTC provides a total examination of the colon in more than 90% of patients, including those with distal occlusive colorectal cancer, the frail and the elderly, and in circumstances of failed or incomplete colonoscopy. However, patients with abnormal results on CTC will still require conventional colonoscopy. Additionally, residual solid stool can simulate a true polyp, and residual liquid also can interfere with test accuracy. A CTC also provides the same information as a noncontrast CT scan of the abdomen and pelvis outside of the colon.

Clinical Trials of CT Colonography. Published data regarding the sensitivity and specificity of CTC are predominantly based on single detector CT technology and have been performed mostly in symptomatic or high-risk patients in a small subset of academic medical centers.

Some studies comparing CTC with conventional colonoscopy have yielded inadequate results in that the specificity for polyps less than 1 cm in size, including those in the 5- to 9-mm range, has been below 70%.65-69 Results of larger studies have found that the sensitivity of CTC for the detection of polyps measuring 10 mm or larger generally ranges from 75% to 100%,70-75 although it was only 50% in the third largest published study.65 In the largest series to date, the per polyp sensitivity was 90.2% for 10 mm or larger, 80.1% for 5 to 9.9 mm, and 59.1% for polyps smaller than 5 mm.70 A recent blinded prospective study in 165 patients with suspected colorectal lesions found CTC to have a diagnostic sensitivity similar to that of conventional colonoscopy for the detection of colorectal lesions ≥ 6 mm in diameter, results that are in agreement with the study of Fenlon et al71 in patients at high risk of colorectal neoplasia.76

The sensitivity of conventional colonoscopy for polyps ≥10 mm using similar study designs has been reported at 94% to 100% and at 87% to 88% for polyps in the 6 to 9 mm range.59,77

Large-scale multicenter trials in patients at average risk are planned and some are currently underway in the United States and Europe to further clarify the usefulness of CTC as a screening test. One such trial has been completed.78 Preliminary results indicated that among 619 subjects ≥50 years of age presenting for elective conventional colonoscopy, the sensitivity of CTC for correctly identifying subjects with at least one 6 mm polyp was 36%, with a specificity of 88%. The corresponding values for 10-mm polyps were 47% sensitivity and 95% specificity. These results suggest that the performance of virtual colonoscopy may be inadequate for the correct detection of 6 mm and 1 cm lesions in such patients.

Comment. CTC relies on the use of state-of-the-art scanners, software analysis, and trained radiologists who are familiar with interpreting these studies. CTC requires colon preparation (like conventional colonscopy) and the insertion of an enema tube to fill the colon with gas. Three multidisciplinary groups that create guidelines on colorectal cancer screening, the American Cancer Society, the United States Multi-Society Task Force on Colorectal Cancer, and the United States Preventive Services Task Force have recently evaluated the data on CTC and concluded that its use for colorectal cancer screening is currently inappropriate.79-81

Routinely, its sensitivity is less than conventional colonoscopy for polyps ≥10 mm in high-risk patients and for smaller sized (ie, 6 to 9 mm) polyps. Its value and performance in average-risk populations in other health care settings is unknown, but preliminary results do not support its widespread use as a screening test. Nearly all studies to date have been intentionally biased to create a cohort with a high prevalence of disease. Studying only high-risk patients overestimates the diagnostic accuracy of a procedure.

Sensitivities below 80% to 85% for polyps sized 5 to 9 mm, and substantially less for polyps <5 mm may be unacceptable for a diagnosis-only screening strategy as expensive as CTC.82 This level of performance would probably increase the frequency at which scans would be required, thereby decreasing cost-effectiveness. Interestingly, in contrast to the lung cancer screening debate, CTC finds polyps later in the growth process but is being promoted as a useful intervention. Although CTC is useful in patients who refuse to undergo colonscopy for various reasons, and there appears to be sufficient evidence to support its use in patients following failed or incomplete colonoscopy, further evaluation in the form of multicenter trials is required before it can compete on a widespread basis as a colonic cancer screening tool. Appropriate targets for studying the diagnostic accuracy of CTC for colorectal cancer screening are asymptomatic, low-prevalence populations that represent a cross-section of the US adult population. Pending further trials, CTC should not be used for routine screening, surveillance, or diagnosis until the numerous uncertainties about its use are clarified.82 The possibility that CTC may be able to be performed without prior bowel preparation is a potential development that would clearly have an impact on its relative utility.

Whole Body Scans

As briefly discussed in the beginning of this report, there is no evidence to date to support the use of a "total body scan" as an appropriate or effective tool in the early detection or prevention of disease. Such services are not evidence-based and are not consistent with accepted guidelines for screening. Back to Top

Conclusion and Comment

Standards for new technology include the development of published evidence where the estimation of patient outcomes must be established in sufficiently large patient samples, with the data rigorously collected and analyzed from a diverse array of patient subsets. Ethical and professional issues are evident in promoting screening techniques with no proven mortality benefit and in not fully informing patients about the uncertain benefits, risks, and potential harms of innovative screening techniques. The use of screening tests generally should be based on a physician’s order to allow for full discussion of these issues, to provide appropriate continuity of care, and to integrate primary prevention and treatment alternatives.

As these tests proliferate, it is appropriate to question the balance among medical science, patient care, and profits. Widespread use of unproven screening tests (or other therapies) lead to spiraling costs of health care. Even if patients pay with their own funds for such screenings, there are financial consequences that affect the rest of the health care system because insurers and health plans are more likely to bear the costs of subsequent evaluations after an abnormal scan. On the other hand, an individual’s right to know his or her health status, access to health care in a free market economy, and other issues based on individual and societal value systems are noteworthy. In such an environment, the medical profession should continue to advocate the use of clinically effective and cost-effective procedures and interventions.

RECOMMENDATIONS
The following statements, recommended by the Council on Scientific Affairs, were adopted by the AMA House of Delegates as AMA Policy and Directives a the 2003 AMA Annual Meeting:

  1. Relevant specialty societies should continue to evaluate the validity and clinical use of screening imaging procedures that are advertised directly to the public and make available to the broader physician community unbiased evaluations to help primary care physicians advise their patients of the risks and benefits of these procedures. (Policy)
  2. The AMA urges government funding agencies to continue to fund well-designed, large-scale clinical trials aimed at determining the safety, value, and cost-effectiveness of screening imaging procedures. (Directive)
  3. Considering the summary information in this report, the Council on Ethical and Judicial Affairs will further consider the ethical ramifications of commercialized medical screening. (Directive)

CSAPH home page
Reports by topic

Table. Characteristics of Follow-up Studies of EBCTa and Coronary Event in Asymptomatic Populations

Study

No.

Mean Age/Sex

Follow-up

Calcium Scores

Baseline Risk for Hard Event

Number of Deaths and nonfatal MIb

RRc for MI or Death if >CACd score

Arad18

1,173

53 yrs

71% men

43 months

Median 4

Not reported

16

22.2 > 160

Raggi19

632

52 yrs

50% men

37 months

Median 3.1; 54% had CAC

10% at 10 yrs

27

7.2, > median for age/sex

3.0, >50th percentile

Detrano20

1,196

66 yrs

89% men

41 months

Median 44

3.3% at 3 yrs

50

2.3, >50thpercentile

Wong21

926

54 yrs

79% men

24-48 months (mean 39)

Median 5

Not reported

28e

4.5, >50th percentile

aEBCT = electron beam computed tomograpy; bMI = myocardial infarction; cRR = relative risk; dCAC = coronary artery calcification; eincludes coronary revascularization procedures

Back to Text

 References

  1. American College of Radiology statement on CT screening exams. Available at www.acr.org/departments/pub_rel/press_releases/total-bodyCT.htm. Accessed March 27, 2003.
  2. Welch HG, Schwartz LM, Woloshin S. Are increasing 5-year survival rates evidence of success against cancer? JAMA. 2000;283:2975-2978.
  3. Wexler L, Brundage B, Crouse J, et al. Coronary artery calcification: pathophysiology, epidemiology, imaging methods, and clinical implications. A statement for health professionals from the American Heart Association. Writing Group. Circulation. 1996;94:1175-1192.
  4. Emond M, Mock MB, Davis KB, et al. Long-term survival of medically treated patients in the Coronary Artery Surgery Study (CASS) Registry. Circulation. 1994;90:2645-2657.Ringqvist I, Fisher LD, Mock M, et al. Prognostic value of angiographic indices of coronary artery disease from the Coronary Artery Surgery Study (CASS). J Clin Invest. 1983;71:1854-1866.
  5. Rumberger JA, Simons DB, Fitzpatrick LA, Sheedy PF, Schwartz RS. Coronary artery calcium area by electron-beam computed tomography and coronary atherosclerotic plaque area. A histopathologic correlative study. Circulation. 1995;92:2157-2162.
  6. O'Rourke RA, Brundage BH, Froelicher VF, et al. American College of Cardiology/American Heart Association Expert Consensus Document on electron-beam computed tomography for the diagnosis and prognosis of coronary artery disease. J Am Coll Cardiol. 2000;36:326-340.
  7. Guerci AD, Spadaro LA, Goodman KJ, et al. Comparison of electron beam computed tomography scanning and conventional risk factor assessment for the prediction of angiographic coronary artery disease. J Am Coll Cardiol. 1998;32:673-679.
  8. Schmermund A, Rumberger JA, Colter JF, Sheedy PF, Schwartz RS. Angiographic correlates of "spotty" coronary artery calcium detected by electron-beam computed tomography in patients with normal or near-normal coronary angiograms. Am J Cardiol. 1998;82:508-511.
  9. Sangiorgi G, Rumberger JA, Severson A, et al. Arterial calcification and not lumen stenosis is highly correlated with atherosclerotic plaque burden in humans: a histologic study of 723 coronary artery segments using nondecalcifying methodology. J Am Coll Cardiol. 1998;31:126-133.
  10. Schmermund A, Denktas AE, Rumberger JA, et al. Independent and incremental value of coronary artery calcium for predicting the extent of angiographic coronary artery disease: comparison with cardiac risk factors and radionuclide perfusion imaging. J Am Coll Cardiol. 1999;34:777-786.
  11. Farb A, Burke AP, Tang AL, et al. Coronary plaque erosion without rupture into a lipid core. A frequent cause of coronary thrombosis in sudden coronary death. Circulation. 1996;93:1354-1363.
  12. Grundy SM, Pasternak R, Greenland P, Smith S Jr, Fuster V. AHA/ACC scientific statement: Assessment of cardiovascular risk by use of multiple-risk-factor assessment equations: a statement for healthcare professionals from the American Heart Association and the American College of Cardiology. J Am Coll Cardiol. 1999;34:1348-1359.
  13. Grover SA, Coupal L, Hu XP. Identifying adults at increased risk of coronary disease. How well do the current cholesterol guidelines work? JAMA. 1995;274:801-806.
  14. Nallamothu BK, Saint S, Bielak LF, et al. Electron-beam computed tomography in the diagnosis of coronary artery disease: a meta-analysis. Arch Intern Med. 2001;161:833-838.
  15. Rumberger JA, Sheedy PF 2nd, Breen JF, Fitzpatrick LA, Schwartz RS. Electron beam computed tomography and coronary artery disease: scanning for coronary artery calcification. Mayo Clin Proc. 1996;71:369-377.
  16. Greenland P, Abrams J, Aurigemma GP et al. Prevention Conference V. Beyond secondary prevention: identifying the high-risk patient for primary prevention; noninvasive tests of atherosclerotic burden. Circulation. 2000;101:e16-e22.
  17. Arad Y, Spadaro LA, Goodman K, Newstein D, Guerci AD. Prediction of coronary events with electron beam computed tomography. J Am Coll Cardiol. 2000;36:1253-1260.
  18. Raggi P, Callister TQ, Cooil B, et al. Identification of patients at increased risk of first unheralded acute myocardial infarction by electron-beam computed tomography. Circulation. 2000;101:850-855.
  19. Wong ND, Hsu JC, Detrano RC, Diamond G, Eisenberg H, Gardin JM. Coronary artery calcium evaluation by electron beam computed tomography and its relation to new cardiovascular events. Am J Cardiol. 2000;86:495-498.
  20. Detrano RC, Wong ND, Doherty TM, et al. Coronary calcium does not accurately predict near-term future coronary events in high-risk adults. Circulation. 1999;99:2633-2638.
  21. Pitt B, Rubenfire M. Risk stratification for the detection of preclinical coronary artery disease. Circulation. 1999;99:2610-2612.
  22. O'Malley PG, Taylor AJ, Jackson JL, Doherty TM, Detrano RC. Prognostic value of coronary electron-beam computed tomography for coronary heart disease events in asymptomatic populations. Am J Cardiol. 2000;85:945-948.
  23. Stephens MB. Is electron-beam computed tomography (EBCT) a reliable tool for predicting coronary outcomes in an asymptomatic population? J Fam Practice. 2000;48:688.
  24. Taylor AJ, Feuerstein I, Wong H, Barko W, Brazaitis M, O'Malley PG. Do conventional risk factors predict subclinical coronary artery disease? Results from the Prospective Army Coronary Calcium Project. Am Heart J. 2001;141:463-468.
  25. Bild DE, Bluemke DA, Burke GL, et al. Multi-ethnic study of atherosclerosis: objectives and design. Am J Epidemiol. 2002;156:871-881.
  26. O'Malley PG, Taylor AJ, Gibbons RV, et al. Rationale and design of the Prospective Army Coronary Calcium (PACC) Study: utility of electron beam computed tomography as a screening test for coronary artery disease and as an intervention for risk factor modification among young, asymptomatic, active-duty United States Army personnel. Am Heart J. 1999;137:932-941.
  27. Feinstein MB, Bach PB. Epidemiology of lung cancer. Chest Surg Clin North Am. 2000;10:653-661.
  28. Frost JK, Ball WC, Levin ML, et al. Early lung cancer detection: results of the initial (prevalence) radiologic and cytologic screening in the Johns Hopkins study. Am Rev Respir Dis. 1984;130:549-554.
  29. Flehinger BJ, Melamed MR, Zana MB, Heelan RT, Perchick WB, Martini N. Early lung cancer detection: results of the initial (prevalence) radiologic and cytologic screening in the Memorial Sloan-Kettering study. Am Rev Respir Dis. 1984;130:555-560.
  30. Fontana R, Sanderson DR, Woolner LB, et al. Lung cancer screening: the Mayo program. J Occup Med. 1986;28:746-750.
  31. Kubik A, Polak J. Lung cancer detection: results of a randomized prospective study in Czechoslovakia. Cancer. 1986;57:2427-2437.
  32. Berlin NI, Buncher CAR, Fontana RS, Frost JK, Melamed MR. The National Cancer Institute Cooperative Early Lung cancer Detection Program: results of the initial screen (prevalence). Am Rev Respir Dis. 1984;130:545-549.
  33. Tockman MS. Survival and mortality from lung cancer in a screened population: the Johns Hopkins Study. Chest. 1986;89(Suppl):324S-325S.
  34. Flehinger BJ, Melamed MR. Current status of screening for lung cancer. Chest Surg Clin North Am. 1994;4:1-14.
  35. Marcus PM, Bergstralh EJ, Fagerstrom RM, et al. Lung cancer mortality in the Mayo Lung Project: impact of extended follow-up. J Natl Cancer Inst. 2000;92:1308-1316.
  36. Ellis JR, Gleeson FV. Lung cancer screening. Br J Radiol. 2001;74:478-485.
  37. Prorok PC, Andriole GL, Bresalier RS, et al. Design of the Prostate, Lung, Colorectal and Ovarina (PLCO) Cancer Screening Trial. Control Clin Trials. 2000;21(6 Suppl):273S-309S.
  38. Kaneko M, Eguchi K, Ohmatsu H, et al. Peripheral lung cancer: screening and detection with low-dose spiral CT versus radiography. Radiology.1996;201:798-802.
  39. Sobue T, Moriyama N, Kaneko M, et al. Screening for lung cancer with low-dose helical computed tomography: anti-lung cancer association project. J Clin Oncol. 2002;20:911-920.
  40. Nawa T, Nakagawa T, Kusano S, Kawasaki Y, Sugawara Y, Nakata H. Lung cancer screening using low-dose spiral CT: results of baseline and 1-year follow-up studies. Chest. 2002;122:15-20.
  41. Sone S, Takashima S, Li F, et al. Mass screening for lung cancer with mobile spiral computed tomography scanner. Lancet. 1998; 351(9111):1242-1245.
  42. Kakinuma R, Ohmatsu H, Kaneko M, et al. Detection failures in spiral CT screening for lung cancer: analysis of CT findings. Radiology. 1999;212:61-66.
  43. Henschke CI, McCauley DI, Yankelevitz DF, et al. Early lung cancer action project: a summary of the findings on baseline screening. Oncologist. 2001;6:147-52.
  44. Henschke CI, McCauley DI, Yankelevitz DF, et al. Early Lung Cancer Action Project: overall design and findings from baseline screening. Lancet.   1999;354:99-105.
  45. Swensen SJ, Jett JR, Sloan JA, et al. Screening for lung cancer with low-dose spiral computed tomography. Am J Respir Crit Care Med. 2002;165:508-13.
  46. Sone S, Li F, Yang ZG, Honda T, et al. Results of three-year mass screening programme for lung cancer using mobile low-dose spiral computed tomography scanner. Br J Cancer. 2001; 84:25-32.
  47. Henschke CI, Yankelevitz DF. CT screening for lung cancer. Radiol Clin North Am 2000; 38:487-95, viii.
  48. Henschke CI, Naidich DP, Yankelevitz DF, et al. Early lung cancer action project: initial findings on repeat screenings. Cancer. 2001;92:153-159.
  49. Patz EF Jr, Black WC, Goodman PC. CT screening for lung cancer: not ready for routine practice. Radiology. 2001;221:587-591.
  50. Diederich S, Wormanns D, Semik M, et al. Screening for early lung cancer with low-dose spiral CT: prevalence in 817 asymptomatic smokers. Radiology. 2002;222:773-781.
  51. Yankelevitz DF, Reeves AP, Kostis WJ, et al. Small pulmonary nodules: volumetrically determined growth rates based on CT evaluation. Radiology. 2000;217:251-256.
  52. Bach PB, Niewoehner DE, Black WC. Screening for lung cancer. The guidelines. Chest. 2003;123:83S-88S.
  53. American College of Radiology Statement on CT Screening Exams (Accessed May 1, 2003 at http://www.acr.org ).
  54. Aberle DR, Gamsu G, Henschke CI, et al. A consensus statement of the Society of Thoracic Radiology: screening for lung cancer with helical computed tomography. J Thorac Imaging. 2001;16:65-68.
  55. Grann VR, Neugut AI. Lung cancer screening at any price? JAMA . 2003;289:357-358.
  56. Winawer SJ, Zauber AG, Ho MN, et al. Prevention of colorectal cancer by colonoscopic polypectomy. The national Polyp Study Workgroup. N Engl J Med. 1993;329:1977-1981.
  57. Rex DK, Rahmani EY, Haseman JH, Lemmel GT, Kaster S, Buckley JS. Relative sensitivity of colonoscopy and barium enema for detection of colorectal cancer in clinical practice. Gastroenterology. 1997;112:17-23.
  58. Rex DK, Cutler CS, Lemmel GT, Rahmani EY, Clark DW, Helper DJ, Lehman GA, Mark DG. Colonoscopic miss rates of adenomas determined by back-to-back colonoscopies. Gastroenterology. 1997;112:24-28.
  59. Smith CS, Fenlon HM. Virtual colonoscopy. Best Pract Res Clin Gastroenterol. 2002; 16:219-236.
  60. Hawes RH. Does virtual colonoscopy have a major role in population-based screening? Gastrointest Endosc Clin North Am. 2002;12:85-91.
  61. Gluecker TM, Fletcher JG. CT colonography (virtual colonoscopy) for the detection of colorectal polyps and neoplasms. current status and future developments. Eur J Cancer. 2002;38:2070-2078.
  62. Bond JH. Colorectal cancer screening: the potential role of virtual colonoscopy. J Gastroenterology. 2002;37(Suppl 13):92-6:92-96.
  63. Dachman AH. Virtual colonoscopy. Potential clinical applications of a new technique. Gastroenterol Clin North Am. 2002;31:747-757.
  64. Miao YM, Amin Z, Healy J, et al. A prospective single centre study comparing computed tomography pneumocolon against colonoscopy in the detection of colorectal neoplasms. Gut. 2000;47:832-837.
  65. Mendelson RM, Foster NM, Edwards JT, Wood CJ, Rosenberg MS, Forbes GM. Virtual colonoscopy compared with conventional colonoscopy: a developing technology. Med J Aust. 2000;173:472-475.
  66. Rex DK, Vining D, Kopecky KK. An initial experience with screening for colon polyps using spiral CT with and without CT colonography (virtual colonoscopy). Gastrointest Endosc. 1999;50:309-313.
  67. Spinzi G, Belloni G, Martegani A, Sangiovanni A, Del Favero C, Minoli G. Computed tomographic colonography and conventional colonoscopy for colon diseases: a prospective, blinded study. Am J Gastroenterol. 2001;96:394-400.
  68. Pescatore P, Glucker T, Delarive J, et al. Diagnostic accuracy and interobserver agreement of CT colonography (virtual colonoscopy). Gut. 2000;47:126-130.
  69. Yee J, Akerkar GA, Hung RK, et al. Colorectal neoplasia: performance characteristics of CT colonography for detection in 300 Patients. Radiology. 2001;219:685-692.
  70. Fenlon HM, Nunes DP, Schroy PC III, Barish MA, Clarke PD, Ferrucci JT. A comparison of virtual and conventional colonoscopy for the detection of colorectal polyps. N Engl J Med. 1999;341:1496-1503.
  71. Hara AK, Johnson CD, MacCarty RL, Welch TJ, McCollough CH, Harmsen WS. CT colonography: single- versus multi-detector row imaging. Radiology. 2001;219:461-465.
  72. Morrin MM, Farrell RJ, Kruskal JB, Reynolds K, McGee JB, Raptopoulos V. Utility of intravenously administered contrast material at CT colonography. Radiology 2000;217:765-771.
  73. Macari M, Bini EJ, Xue X, et al. Colorectal neoplasms: prospective comparison of thin-section low-dose multi-detector row CT colonography and conventional colonoscopy for detection. Radiology. 2002;224:383-392.
  74. Fletcher JG, Johnson CD, Welch TJ, et al. Optimization of CT colonography technique: prospective trial in 180 patients. Radiology. 2000;216:704-711.
  75. Laghi A, Iannaccone R, Carbone I, et al. Computed tomographic colonography (virtual colonoscopy): blinded prospective comparison with conventional colonoscopy for the detection of colorectal neoplasia. Endoscopy. 2002;34:441-446.
  76. Hixson LJ, Fennerty MB, Sampliner RE, McGee D, Garewal H. Prospective study of the frequency and size distribution of polyps missed by colonoscopy. J Natl Cancer Inst. 1990;82:1769-1772.
  77. Cotton PB, Durkalski VL, Palesch YY, et al. Comparison of virtual colonoscopy and colonoscopy in the detection of polyps/masses. Gastrointest Endosc. 2002;55:AB98.
  78. Winawer S, Fletcher R, Rex D, et al. Colorectal cancer screening and surveillance: clinical guidelines and rationale-Update based on new evidence. Gastroenterology. 2003;124:544-560.
  79. Levin B, Brooks D, Smith RA, Stone A. Emerging technologies in screening for colorectal cancer: CT colonography, immunochemical fecal occult blood tests, and stool screening using molecular markers. CA Cancer J Clin. 2003;53:44-55.
  80. Pignone M, Rich M, Teutsch SM, Berg AO, Lohr KN. Screening for colorectal cancer in adults at average risk: a summary of the evidence for the U.S. Preventive Services Task Force. Ann Intern Med. 2002;137:132-141.
  81. Rex DK. Barium studies/virtual colonoscopy: the gastroenterologist's perspective. Gastrointest Endosc. 2002;55(7 Suppl):S33-36.
Resolution 508 (I-01) and Resolution 509 (A-02)

Resolution 508 (I-01), introduced by the Young Physicians Section and referred to the Board of Trustees (BOT) for decision, asked: (1) that the American Medical Association (AMA) study the marketing and use of commercial medical screening tests for the general public when not recommended by the patient’s physician and when performed without physician directives; (2) that the AMA consider developing standards based upon the results of its study; and (3) that the AMA report back to the House of Delegates (HOD) at the 2002 Interim Meeting. At the April 2002 meeting of the BOT, a decision was made to forward a BOT report on this issue to the HOD.

Resolution 509 (A-02), introduced by the Wisconsin Delegation and also referred to the BOT, asked: (1) that the AMA establish as policy that it is inappropriate for physicians to be involved in promoting commercialized screening procedures to the public, unless supported by evidence-based guidelines supporting such screenings; (2) that the AMA undertake a public education campaign using existing publications including the Web site explaining the criteria for effective screening; and (3) that the AMA encourage the public to seek appropriate health screening.

Because the issues raised in these two resolutions are related they were considered together in developing an AMA Board of Trustees (BOT) Report. Subsequently, the BOT reconsidered its decision to provide a report to the House of Delegates and requested instead that both the Council on Scientific Affairs and the Council on Ethical and Judicial Affairs address these resolutions. As the first step, the CSA agreed to briefly evaluate the scientific basis of these resolutions in the context of generally accepted criteria for screening. Most of the practices in question involve the use of high-technology, noninvasive imaging scans. Back to Text

CSAPH home page
Reports by topic

Last updated: Feb 21, 2008
Content provided by: CSAPH