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The accuracy of those proliferating screening programs.

The accuracy of those proliferating screening programs

MLO's four-part series continues with an evaluation of the precision of current testing, the training required, participant education and referral, and impending regulation.

Although the role of cholesterol in the development of atherosclerosis has been scientifically scrutinized since 1912, some aspects remain controversial.[1] Experts have debated two factors in particular: the role of diet in determining blood cholesterol levels and the role of blood cholesterol levels in determining the risk of coronary artery disease (CAD).[2-5]

Accordingly, in 1984 the National Institutes of Health convened a consensus development panel to examine the role of blood cholesterol in heart disease. After examining the available evidence, the panel concluded that high blood cholesterol levels are a major cause of CAD; that lowering blood cholesterol levels will reduce CAD risk; that vigorous treatment should be available for people in the top 25 per cent of cholesterol distribution; and that to lower their blood cholesterol levels, all Americans should adopt a diet including less overall fat, saturated fat, and dietary cholesterol.[6]

The panel's report was not the first public policy statement to define a causal link between diet and blood cholesterol levels and thus between those levels and CAD risk.[7,8] Yet its thorough review of genetic factors, metabolic research ward studies, clinical trials, and epidemiologic studies represented a landmark in the evolution of Federal public health policy in this area.

Of special note is the panel's having gone beyond recommending an approach to cholesterol management for those at high risk for coronary artery disease--to include physician referral, the initiation of phased diets, and, when indicated, pharmacologic therapy--to address the broader issues of high rates of CAD, a distribution of blood cholesterol levels that contributes to this risk, and a typical high-fat diet that predisposes the U.S. population to such elevated levels.

* National effort. A major outcome of the consensus conference was the establishment of the National Cholesterol Education Program (NCEP) within the National Heart, Lung, and Blood Institute (NHLBI).[9] Among the NCEP's first acts was to establish four panels to investigate more thoroughly certain issues critical to the successful implementation of a national campaign to lower blood cholesterol levels nationwide. The four NCEP panels have focused on the detection, evaluation, and treatment of high blood cholesterol in adults and in children and adolescents, laboratory standardization, and approaches for the general population.

The Expert Panel on the Detection, Evaluation, and Treatment of High Blood Cholesterol in Adults presented its report several years ago.[10,11] The report, which builds on the work of the consensus development conference, reflects later knowledge about high blood cholesterol and its treatment. In addition, the report provides detailed recommendations for treating high blood cholesterol levels in adults. The panel's major recommendations are summarized in Figure I.

According to the panel, the desired blood cholesterol level is 200 mg/dl or lower. A borderline high level falls between 200 mg/dl and 239 mg/dl. Considered high is a level of 240 mg/dl and above. A low-density lipoprotein (LDL) cholesterol level of 160 mg/dl or greater was found to indicate a high-risk profile useful to physicians in planning treatment. Treatment decisions are to take into account such individual patient characteristics as male sex (itself a proven risk factor for coronary artery disease), family history of premature CAD, cigarette smoking, hypertension, low concentration of high-density lipoprotein (HDL) cholesterol, diabetes mellitus, personal history of cerebrovascular or occlusive peripheral vascular disease, and severe obesity (30 per cent or more overweight).

The presence of other CAD risk factors, particularly important in treatment decisions for patients with a borderline high cholesterol level, represents another important consideration. Studies have demonstrated that the percentage of coronary stenosis and the incidence of CAD mortality are not only affected by the blood cholesterol level but also multiplied by the addition of other risk factors for CAD.[12,13]

The implications of these criteria for the U.S. population were recently documented by Sempos and coworkers.[14] Using data from the National Health and Nutrition Examination Survey II, conducted from 1976 to 1980, these authors found that 41 per cent of the U.S. adult population would require follow-up lipoprotein analyses based on a single blood cholesterol value. In addition, as many as 60 million Americans might require treatment for a high blood cholesterol level. Clearly, high blood cholesterol levels in the nation's population is a problem that will require concerted and coordinated action by professionals in virtually all sectors of the health care field.

* Conceptual model. A healthy outgrowth of public awareness campaigns and mass media attention to the cholesterol issue has been a groundswell of interest and activity in blood cholesterol screening programs. The primary objectives of these programs have been to identify persons with elevated blood cholesterol levels and to refer them for appropriate treatment. The rationale for such screening programs meets accepted standards as established by Berwick[15]: that there should be a sufficient prevalence of a disease or condition to warrant screening activities; that such conditions are unlikely to be detected without screening; that low-cost screening protocols are available; that the screening program is both sensitive and specific (i.e., has a low rate of error); and that treatment for the condition is available, beneficial, and broadly acceptable.

While substantial data support the first two points, low-cost testing was not available until the advent of portable desktop clinical analyzers. Programs offering information to physicians will help insure that they understand the need to make effective treatment available to every patient identified as having an elevated blood cholesterol level.

In undertaking cholesterol screening, many programs attempt to follow the traditional "disease detection" (DD) method, in which the goal is to identify cases and to refer them for appropriate treatment, usually to a physician. In contrast, some health professionals believe that to make a public health impact on cholesterol levels, screening programs should adopt a "risk factor" (RF) identification approach, as outlined by Safer.[16]

In the RF model, joint goals of screening are to identify risk factors and to initiate changes in behavior. Rather than viewing referral as the primary outcome for screening programs, the RF approach assesses participants' risk and provides them with educational opportunities and counseling for modifying specific factors.

Another difference between the two approaches is the way in which they are evaluated. In the DD model, effectiveness is based upon whether physician referral is made, the participant acts on the referral, successful treatment is initiated, and the process results in a cost-effective way to reduce cardiovascular morbidity and mortality. With the RF approach, evaluation includes an assessment of knowledge, attitude, and behavior change with respect to their impact on the lowering of the blood cholesterol level, and a subsequent reduction in cardiovascular morbidity and mortality. Determining whether this method is sufficiently cost-effective will require further examination.[17-19]

* Screening tips. In October 1988 the NHLBI brought together scientists and practitioners with experience in cholesterol screening to compile a series of practical recommendations for providers of public screening for high blood cholesterol. The panel's recommendations, released at the First National Cholesterol Conference in November 1988, were recently published.[20] The report include suggestions for recruiting participants, measuring cholesterol levels reliably, and training staff members. The recommendations on appropriate participant education and referral are particularly noteworthy.

Following the risk factor identification approach, the panel's report stresses the importance of providing to all screening participants information about cholesterol and its relationship to coronary artery disease. Also emphasized is that referrals to medical care must be based on cholesterol level results and an assessment of CAD risk factors. A key point is that the new technologies can provide accurate measurements of blood cholesterol if performed by a well-trained staff.

The workshop report stresses the importance of making sure that blood cholesterol measurements obtained in screening programs are accurate. This emphasis is consistent with the recommendations developed by the NCEP's Laboratory Standardization Panel (LSP).[21]

* Insuring accuracy. Screenings to determine blood cholesterol levels provide a useful tool in reaching the public health objective of lowering such levels in the entire population of the United States, not just identifying high-risk individuals. The more sweeping goal is largely made possible by the relatively low cost and the widespread public acceptance of blood cholesterol screening programs across the country.

The call to "know your cholesterol number" has been heeded by the nearly 50 per cent of the U.S. population who have had their cholesterol levels checked.[22] Nonetheless, only 7 per cent of the population know their number; extensive education remains to be given. Doing so will require the skillful application of demonstrated principles of social marketing.[23]

The LSP report on the current status of lipid measurement used various studies and data sources to highlight the major areas of concern. Surveys by the College of American Pathologists, for example, have found that the precision of cholesterol assays--that is, the ability of one laboratory to reproduce similar results on the same specimen--has steadily improved. Coefficients of variation (CVs) of 3.5 per cent can thus be expected within the laboratory; CVs of 6.2 per cent are now possible from one laboratory to another.

While these figures have been averaged from the more than 5,000 laboratories that participated in the survey, this database also shows that different laboratory instruments show a wide range of values when compared with a sample having a reference value set by the Centers for Disease Control. In the 1985 CAP survey, for instance, when laboratories measured a CDC reference sample of 262.6 mg/dl, results ranged from 197 mg/dl to 300 mg/dl. Such variability in cholesterol measurements requires immediate correction.

According to LSP recommendations, laboratories should attain accuracy within [+ or -] 5 per cent of a known value. An objective for 1990 is to reduce this bias to [+ or -] 3 per cent. Results from the Lipid Research Clinics (LRC) Program suggest that it will be possible to meet these high expectations. The 12 LRC laboratories were able to achieve an overall bias of - 1.3 per cent when compared with CDC reference values. Day-to-day reproducibility (precision) of [is less than or equal to] 3 per cent CV was maintained over many years.

* Implications. Since patients who have cholesterol levels of 240 mg/dl or higher are referred to physicians for follow-up, referral decisions will be significantly affected by a method bias. With an acceptable bias of [+ or -] 5 per cent, the cholesterol measurement for an individual with a 240 mg/dl total cholesterol level could range from 216 mg/dl to 264 mg/dl; a bias of 3 per cent reduces this range to 226 to 254 mg/dl.

The large disparity documents the current inadequate status of lipid measurement while high-lighting the responsibility of screening protocols not to allow a screening result to be presented as an absolute value. Furthermore, those in a position to counsel participants must stress that results from an initial screening cannot be equated with a diagnosis of hypercholesterolemia. Decisions concerning diagnosis and treatment must be based on at least two measurements of the blood cholesterol level.

As laboratories work to fall into line with the LSP recommendations, studies are documenting the ability of several brands of portable desktop analyzers to meet the levels of precision recommended by the LSP.[24-26] Researchers have noted, however, that only careful attention to quality control protocols will assure that the instruments will provide accurate measurements--a stand echoed in the Screening Workshop report. In all cases, QC protocols should be developed and implemented with the advice and technical expertise of the staff of a local clinical laboratory.

* Regulatory control. Issues of quality control are equally important for blood cholesterol measurements that are obtained in physicians' office laboratories. The call by the U.S. Preventive Services Task Force for periodic measurement of blood cholesterol levels, especially among middle-aged men,[27] will lend further impetus to office-based screening protocols.

The current paucity of state regulation over POLs, coupled with data showing marked variability among office laboratories in proficiency testing performance, suggests that much more attention needs to be given to insuring reliable and accurate test results in this environment.[28] It remains to be seen exactly how the Clinical Laboratory Improvement Amendments of 1988 will affect blood cholesterol measurements taken in physicians' office labs and non-traditional sites.[29]

* State regulation. In many states, regulating blood cholesterol screenings has become an important concern. Several states were prepared because applicable regulations and policies were already in place. (In some states, such policies have been called overly restrictive.)

Most states, however, were caught off guard by the new technology and its rapid deployment. As they now struggle to catch up, they must attempt to balance consumer benefits and risks, professional roles and responsibilities, and economic costs and public health. These states will look to the NCEP guidelines for public screening programs as a model from which to fashion regulations that meet the needs of their constituencies.

Public policy in this area has developed quickly. Yet a cool-eyed, even-handed approach can bring local governments up to the mark--provided that they meet established criteria for staff training, QC, and participant education and referral.

* HDL cholesterol. Screening HDL cholesterol has been discussed extensively, especially concerning the value of technologic innovations and the extent of consumer demand. Arguments that the public has a right to know are counterbalanced by strong concerns for a far more deliberate and cautious approach to whether the screening is always valid.

Returning to Berwick's criteria for screening programs raises three questions:

1. Is low HDL cholesterol sufficiently widespread to warrant screening? Evidence leads to the conclusion that routine measurement of HDL cholesterol in otherwise completely healthy individuals not at risk for CAD "is likely to uncover a relatively small number of cases."[30]

2. Is the screening procedure both sensitive and specific? This question cannot be answered at present because methods for estimating HDL cholesterol have not been well standardized. In fact, it may be three to five years before this goal is reached.[30] No method for measuring HDL cholesterol is standard for all instruments and laboratories; therefore, sensitivity and specificity cannot be gauged in any rational way.

3. Is treatment for low HDL cholesterol levels available, advantageous, and acceptable? Reducing one's weight, increasing aerobic activity, and stopping cigarette smoking may all contribute to a slight rise in HDL cholesterol levels.[30] Unless the LDL cholesterol level places the person at high risk (above 160 mg/dl), drug intervention for low HDL cholesterol (below 35 mg/dl) is not recommended at this time.

Where LDL cholesterol should be lowered and drug therapy is indicated, the use of gemfibrozil and/or nicotinic acid should be considered. The way to lower high blood cholesterol levels and thus reduce risk for coronary artery disease is to lower LDL cholesterol levels. This is the message that needs to be placed more prominently before patients and the general public.

Should people be screened for low HDL cholesterol levels? No. Such activity properly belongs in a physician's office within the context of making treatment decisions for patients who have high blood cholesterol levels. To do otherwise offers little to screenees and could in fact discourage people from seeking necessary medical treatment.

* Laboratory's role. For laboratorians, foremost among the challenges and opportunities in blood cholesterol screening is whether such screenings are effective: That is, do they increase people's awareness of their own cholesterol levels, contribute to a lowering of the mean population value of blood cholesterol, and help reduce the prevalence of CAD? A number of research projects are seeking answers to these questions. Meanwhile, the primary focus must be to insure that blood cholesterol screening programs provide accurate and reliable results. Clinical laboratories can help in several ways.

First, clinical labs must meet the current national goals for precision and accuracy in measuring blood cholesterol levels. Unless local laboratories adopt those standards, analytic biases will perpetuate the confusing variability in blood cholesterol levels. A continued discrepancy would undermine the public's confidence in our ability to contribute to their well-being.

Second, clinical laboratories should identify and collaborate with groups conducting blood cholesterol screenings in their communities. Our message to screeners is to work with clinical laboratories in an ongoing relationship to develop, implement, and monitor their quality control protocols. Clinical laboratories must be ready to work with these groups, provide technical assistance as necessary, and serve as the "gold standard" for screening results. Participating in the National Reference System for Cholesterol established by the National Committee for Clinical Laboratory Standards is an important step for full involvement in the process of educating the general public about blood cholesterol levels.

Finally, clinical laboratories should serve as the local sentinels for high-quality screening programs. Plenty of people involved in the cholesterol screening business have minimal experience and expertise. Clinical laboratories need to be alert to screening activities, question those who set up and operate screening programs in their areas, educate screeners when necessary, and help stop those whose only intent is to make a profit rather than to perform a public service. Naturally, any clinical laboratory that conducts blood cholesterol screenings should subscribe to the highest standards as well.

[1]McGill, H.C. The relationship of dietary cholesterol to serum cholesterol concentration and to atherosclerosis in man. Am. J. Clin. Nutr. 32: 2664-2702, 1979. [2]Kaplan, R.M. The connection between clinical health promotion and health status: A critical overview. Am. Psychol. 39: 755-765, 1979. [3]Lefebvre, R.C. Diet, lipids, and coronary heart disease. Am. Psychol. 40: 96-98, 1986. [4]Oliver, M.F. The cholesterol-coronary question: Why not a policy of selective intervention? Int. J. Cardiol. 4: 201-206, 1983. [5]Stamler, J. The prevention and control of epidemic coronary heart disease: Scientific foundations and strategic approaches. Int. J. Cardiol. 4: 207-215, 1983. [6]Consensus Conference: Statement on lowering blood cholesterol to reduce coronary heart disease. JAMA 253: 2080-2086, 1985. [7]Atherosclerosis Study Group: Optimal resources for primary prevention of atherosclerotic diseases. Circulation 70: 157A-205A, 1984. [8]"Report of the WHO Expert Committee on Prevention of Coronary Heart Disease." Geneva, World Health Organization, Technical Series No. 678, 1982. [9]Lenfant, C. A new challenge for America: The National Cholesterol Education Program. Circulation 73: 299-315, 1986. [10]Cleeman, J.I., and Lenfant, C. New guidelines for the treatment of high blood cholesterol in adults from the National Cholesterol Education Program: From controversy to consensus. Arteriosclerosis 7: 649-650, 1987. [11]Report of the National Cholesterol Education Program Expert Panel on detection, evaluation, and treatment of high blood cholesterol in adults. Arch. Intern. Med. 148: 36-69, 1988. [12]Grundy, S.M. Cholesterol and coronary heart disease: A new era. JAMA 256: 2849-2858, 1986. [13]Stamler, J.; Wentworth, D.; and Neaton, J.D. is relationship between serum cholesterol and risk of premature death from coronary heart disease continuous and graded? Findings in 356,222 primary screenees of the Multiple Risk Factor Intervention Trial (MRFIT). JAMA 256: 2823-2828, 1986. [14]Sempos, C.; Fulwood, R.; Haines, C.; et al. The prevalence of high blood cholesterol levels among adults of the United States. JAMA 262: 45-52, 1989. [15]Berwick, D.M. Screening in health fairs: A critical review of benefits, risks, and costs. JAMA 254: 1492-1498, 1985. [16]Safer, M.A. A comparison of screening for disease detection and screening for risk factors. Health Educ. Res. Theory Prac. 1: 131-138, 1986. [17]Ockene, J.K.; Sorensen, G.; Kabat-Zinn, J.; et al. Benefits and costs of lifestyle change to reduce risk of chronic disease. Prev. Med. 17: 224-234, 1988. [18]Oster, G., and Epstein, A.M. Primary prevention and coronary heart disease: The economic benefits of lowering serum cholesterol. Am. J. Public Health 76: 647-656, 1986. [19]Russell, L.B. "Is Prevention Better Than Cure?" Washington, D.C., Brookings Institution, 1986. [20]U.S. Department of Health and Human Services: "Recommendations Regarding Public Screening for Measuring Blood Cholesterol." Washington, D.C., U.S. Government Printing Office, Public Health Service (NIH Pub. No. 89-3045), 1989. [21]Current status of blood cholesterol measurement in clinical laboratories in the United States: Report from the Laboratory Standardization Panel of the National Cholesterol Education Program. Clin. Chem. 34: 193-201, 1988. [22]Schucker, B.; Bailey, K.; Heimbach, J.T.; et al. Change in public perspective on cholesterol and heart disease: Results from two national surveys. JAMA 258: 3527-3531, 1987. [23]Lefebvre, R.C., and Flora, J.A. Social marketing and public health intervention. Health Educ. Q. 15: 299-315, 1988. [24]Lasater, T.M.; Lefebvre, R.C.; Assaf, A.R.; et al. Rapid measurement of blood cholesterol: Evaluation of a new instrument. Am. J. Prev. Med. 3: 311-316, 1987. [25]Lefebvre, R.C.; Lasater, T.M.; McKinlay, S.W.; et al. Performance characteristics of a blood cholesterol measuring instrument used in screening programs. Pub. Health Rep. 104: 266-270, 1989. [26]Burke, J.J., and Fischer, P.M. A clinician's guide to the office measurement of cholesterol. JAMA 259: 3444-3448, 1988. [27]U.S. Preventive Services Task Force. Screening for high blood cholesterol. In: "Guide to Clinical Preventive Services." Washington, D.C., U.S. Department of Health and Human Services, 1989. [28]Crawley, R.; Belsey, R.; Brock, D.; et al. Regulation of physicians' office laboratories: The Idaho experience. JAMA 255: 374-382, 1986. [29]"Clinical Laboratory Improvement Amendments of 1988." Washington, D.C., Congressional Record, H9866-H9872, Oct. 6, 1988. [30]Grundy, S.M.; Goodman, D.S.; Rifkind, B.M.; et al. The place of HDL in cholesterol management: A perspective from the National Cholesterol Education Program. Arch. Intern. Med. 149: 505-510, 1989.

R. Craig Lefebvre is director of the Cholesterol Training Center, division of health education, Memorial Hospital of Rhode Island, Pawtucket, R.I., and assistant professor of community health, Brown University, Providence.
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Title Annotation:Cholesterol Screening, part 2
Publication:Medical Laboratory Observer
Date:Mar 1, 1990
Previous Article:'Diff/if': a differential policy that works.
Next Article:Impress your inspectors with linearity graphs.

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