(Circulation. 1997;95:1642-1645.)
© 1997 American Heart Association, Inc.
Articles |
From the Veterans Affairs Palo Alto Health Care System and Stanford University (A.M.G.), Stanford, Calif; and San Francisco Department of Veterans Affairs Medical Center and University of California, San Francisco (W.S.B.).
Correspondence to Alan M. Garber, MD, PhD, 204 Junipero Serra Blvd, Stanford, CA 94305. E-mail garber{at}camis.stanford.edu.
Key Words: cholesterol tests hypercholesterolemia
| Introduction |
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The ACP produced new cholesterol guidelines as part of a periodic review of all of its guidelines. The updated guidelines and background paper3 focused on the questions addressed in the original background paper and guidelines4 5 : Which adults should undergo screening for lipoprotein disorders? What tests should be used initially? These questions are more narrowly focused than the range of issues addressed in the NCEP report,6 which considered not only the initial screening test but also the sequence of follow-up testing, the criteria for initiation of treatment, and the choice of interventions. Because the effectiveness of screening depends on the steps taken after the result of the screening test is obtained, the ACP implicitly considered some of these issues, but the additional steps were not the subject of recommendations. Thus, the task force mistakenly inferred that the ACP recommended against certain practices proposed by the NCEP (eg, measuring lipoprotein levels in patients with elevated total cholesterol levels) that were not explicitly addressed because they fell outside of the purview of the guidelines.
| Evidence-Based and Consensus-Based Approaches to Guideline Development |
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Consensus- and evidence-based approaches are not a strict dichotomy, and most current guidelines contain elements of each. Although it adhered to a consensus process, the NCEP reviewed a vast amount of evidence and used logic similar to that of the ACP in development of its treatment recommendations; the magnitude of the NCEP effort is manifest in the excellence of their report,6 which is useful even to those who do not agree with all of its recommendations. Unlike some groups that apply evidence-based approaches, the ACP did not rely solely on data from clinical trials. Furthermore, the ACP sought to gain many of the advantages of a consensus process by incorporating extensive internal and external reviews. Because much of the evidence reviewed by both the ACP and the NCEP was clear cut, the two sets of recommendations share many features, including advocacy of an aggressive approach to secondary prevention and testing patients at high risk.
We believe that the critical differences between the cholesterol screening recommendations of the NCEP and ACP result from two features that distinguish evidence- and consensus-based approaches to guideline development: adherence to quantitative inferences drawn from clinical and epidemiological data, and burden of proof. The NCEP report drew heavily on the biological and clinical plausibilities of potential benefit in arguing for aggressive approaches to the detection of hypercholesterolemia. In applying an evidence-based approach to guideline development, the ACP also argued that there might be a benefit from cholesterol detection and treatment but, unlike the NCEP, tried to quantify the benefit. The background paper for the ACP guidelines contained a review of epidemiological data and a description of the results (eg, magnitude of cholesterol reduction, odds ratios for coronary heart disease [CHD] death and total mortality) of every identified randomized, controlled clinical trial of cholesterol reduction that reported clinical outcomes, along with the results of every major reported meta-analysis. To quantify benefits in the large segments of the population excluded from the clinical trials, we estimated the hypothetical reduction in risk of CHD and total mortality resulting from cholesterol reduction in various demographic groups and at various risk levels. The body of evidence supporting the ACP guidelines was culled from an extensive effort to identify relevant information (largely based on Medline searches for clinical trials of cholesterol reduction and epidemiological studies of cholesterol as a risk factor, articles cited in other articles and book chapters, government reports, and citations from reviews and experts who reviewed draft manuscripts). The ACP guidelines are not based on a repudiation of the rationale the NCEP offered but rather represent an attempt to carry it a step further by answering a quantitative question that the NCEP did not answer directly: How great are the likely benefits of cholesterol reduction in specific population groups?
The second feature that distinguishes consensus-based from evidence-based guidelines is the burden of proof for establishing effectiveness: Evidence-based guidelines nearly always place that burden on those who advocate a preventive intervention. Consensus-based guidelines, particularly when they are produced by advocates for a particular set of approaches, may require less direct evidence or only a rationale that supports a potential benefit. Evidence-based approaches to guideline development often require clinical trial evidence of benefit or other directly applicable data. In the absence of acceptable evidence, they may refrain from making recommendations.
The areas in which cholesterol screening recommendations differ clearly illustrate the consequences of adopting either a consensus- or an evidence-based approach. The NCEP and the Canadian Consensus Conference on Cholesterol,8 both of which are consensus groups, recommended universal cholesterol testing in adults, whereas every major group in North America that rated the quality of evidence or attempted to quantify benefits (ie, the US Preventive Services Task Force9 ; the Canadian Task Force on the Periodic Health Examination10 ; the groups that created the official guidelines for the provinces of Ontario,11 Quebec,12 and Saskatchewan13 ; and many provider groups, such as Kaiser-Permanente, and other state or provincial authorities) made screening recommendations similar to those of the ACP.
There are many reasons for the ascendancy of evidence-based approaches to guideline development. Forceful recommendations to carry out screening and other preventive measures in the absence of equally strong evidence that they are beneficial, particularly when the magnitude of the potential benefit is small, can subsequently be proven wrong. The first Adult Treatment Panel of the National Cholesterol Education Program, for example, made stronger recommendations concerning the treatment of elevated cholesterol levels in asymptomatic adults than the subsequent panel14 and may have led to the increased use of gemfibrozil.15 Recent analyses of clinical trial data have concluded that gemfibrozil and other fibrates increase mortality.16 Like most groups that produce guidelines today, we believe that the most appropriate course is to prudently interpret existing data rather than to anticipate the results of future studies. If such studies confirm current hopes about the effectiveness of screening, the ACP should review its guidelines and revise them as appropriate.
| ACP Guidelines: Approach and Content |
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It is in the area of screening people without symptomatic CHD or
vascular diseaseprimary preventionthat the NCEP screening
recommendations differ from those of the ACP and other groups.
Screening can be effective only if treatment is effective. Clinical
trials of cholesterol reduction for primary prevention in middle-aged
men have shown that cholesterol reduction reduces the incidence of CHD,
but until the West of Scotland Study was performed,17 none
showed a survival benefit. Results of primary prevention trials in
women or younger or older men have not been reported. Approaches to
guideline development that require direct evidence of benefit from
clinical trials would recommend neither treatment nor screening in
these excluded groups, particularly because there are several reasons
to question whether their benefits would be as large as they are for
high-risk middle-aged men. The control group of the West of Scotland
Study, for example, died as a result of CHD at a rate
100-fold as
great as that for young women. Secondary prevention trials include even
higher-risk populations: the control group of the Scandinavian
Simvastatin Survival Study (4S) died as a result of CHD at a rate
400-fold as great as that for young women.18 Among
younger people, who have little CHD to prevent, harms that occurred too
infrequently to be detected in these trials could exceed the benefits
of treatment. Although our analysis of individual-level data from the
Framingham Heart Study used assumptions favorable to treatment, it
confirmed this conclusion. In young men, the short-term risk of CHD
from an elevated cholesterol level is only slightly elevated,
particularly in the absence of multiple risk factors for CHD. In young
women, the incidence of CHD is so low that the increase in risk from an
elevated cholesterol level is nearly unmeasurable. Thus, there is
little potential short-term gain from the detection and treatment of
hypercholesterolemia in most young men or women, particularly those who
have no other risk factors for CHD.
The assumption underlying much of the document of the Task Force is
that detection and treatment of hypercholesterolemia in young adults
provide substantial long-term benefits. Nowhere is the difference in
adherence to evidence-based processes more apparent than here. It might
be worth detecting an elevated cholesterol level if dieta safe
interventioncould provide even a modest reduction in the longer-term
risk of CHD. No published clinical trial has directly tested the
effects of cholesterol reduction in young adults, but numerous studies
of experimental diets conducted in metabolic wards, in
institutionalized populations, or among survivors of myocardial
infarction have shown that diet can substantially lower cholesterol
levels. However, in community settings, large, well-designed trials of
diets that would be recommended to most individuals found to have high
cholesterol levels have consistently reported that cholesterol
reduction averages only
2%.19 Thus, despite individual
exceptions, most asymptomatic people will fail to attain
"desirable" cholesterol levels with diet alone, so for most young
people, sustained and large reductions in cholesterol levels will
require more aggressive therapy.
Although drug therapy reduces cholesterol levels more
consistently and substantially, the assumption that early treatment
will have a net benefit has not been established. Even if treatment
initiated in young adulthood is completely safe, it is not likely to
provide great benefits. The risk of CHD falls dramatically within
2
years of the initiation of cholesterol-lowering therapy, even if
started in persons who already have symptomatic CHD; the full potential
benefits of cholesterol reduction appear to be achieved within
5
years of the start of therapy.20 Because the purpose of
cholesterol reduction in young adults is to prevent the occurrence of
CHD in the distant future, the rapid reduction in CHD risk implies that
initiation of screening (and treatment)
5 years before the risk of
CHD becomes substantial will produce essentially all of the benefits
without the additional expense and potential harm of early initiation
of screening. With the recognition that the incidence of CHD begins to
rise at age 40 in men and age 50 in women, the ACP concluded that
cholesterol screening was appropriate beginning at age 35 in men and
age 45 in women without other CHD risk factors or at earlier ages if
other risk factors were present.
Although the Task Force claimed that the ACP guidelines will miss some persons who might benefit from cholesterol reduction, such as young men and women with familial hypercholesterolemia who have no family history, xanthomas, xanthelasma, or other clinical evidence of the disorder, it is not evident that universal screening should be recommended to detect rare conditions (the situation they describe, although too uncommon for reliable statistics, is far less frequent than the overall 1:500 prevalence of familial hypercholesterolemia), particularly when there is no direct evidence that earlier initiation of treatment improves health outcomes.
The Task Force proposed another reason to perform cholesterol screening
in the young: to promote desirable behavioral change, regardless of the
cholesterol level. Available studies, however, show that screening
causes persons to lower their cholesterol levels by only
2% to 4%
during brief follow-up; these modest effects are likely to diminish
over time.21 22 23 24 25 Thus, existing data do not indicate that
cholesterol screening is a particularly effective way to promote
behavioral change. Had this been a reason to screen, the NCEP might
have recommended that this form of behavioral reinforcement be applied
far more frequently than every 5 years.
Noting the lack of relevant clinical trials and ambiguity in the epidemiological data, the ACP refrained from making a recommendation for or against cholesterol screening for primary prevention in the age range of 65 to 75. However, it recommended against screening for primary prevention in men and women age 75 or older. In this group, which is well outside the age range included in primary prevention trials, evidence from epidemiological studies suggests that cholesterol may no longer be a risk factor for CHD.
When direct information about effectiveness is unavailable, such as for cholesterol reduction in young people or the elderly, different approaches may lead thoughtful persons to adopt differing positions. But we are concerned that the Task Force report and the LaRosa commentary that it recapitulates go beyond differences in opinion or interpretation and make statements about the ACP guidelines and the scientific literature that may be misleading. For example, the Task Force claims that the ACP overlooked evidence, such as the fact that cholesterol levels in young adults predict midlife CHD, that was cited and discussed in the background paper. The statement that the ACP displayed ignorance of the fact that a substantial portion of preventable CHD first manifests itself as sudden death or disabling myocardial infarction was not only incorrect but also irrelevant. The comment would be germane if the ACP had restricted cholesterol measurement to patients with CHD, but the ACP recommends screening for primary prevention in many circumstances.
The Task Force misleadingly conflates the results of primary and secondary prevention trials and misrepresents their findings. For example, it claimed that "data from both primary and secondary prevention trials ... demonstrate that cholesterol lowering is just as effective in persons older than 60 years as in younger populations." In support of this statement, the Task Force cites the 4S trial, a secondary prevention study, and the West of Scotland Study. The 4S trial reported the effects of simvastatin in individuals older and younger than age 60; in those younger than 60, the relative risk of a "major coronary event" in treated patients was 0.61, whereas in those older than 60, the relative risk was 0.73, suggesting, if anything, that the relative risk reduction diminishes with age. Although this does not imply that the absolute reduction in risk declines to the oldest age included in the trial (70 years), it reinforces the findings of epidemiological studies that the association between cholesterol and CHD declines with advancing age. The West of Scotland Study, the cited primary prevention trial, did not present the results claimed by the Task Force (the top age of enrollment was 64), but it also reported that the relative risk reduction from the intervention was less in the older participants. The results of these trials support the ACP guidelinesthey suggest that cholesterol reduction may not be as beneficial, particularly for primary prevention, at advanced ages (75 and older). The key point, however, is that all of the participants in these two important trials fell into categories for which the ACP guidelines indicate that cholesterol measurement is appropriate: they had or were at high risk of developing CHD.
| Differences and Similarities |
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Although they were not an explicit factor in the development of
the ACP recommendations, cost-effectiveness considerations lend further
support to targeted screening. Both the NCEP report and the ACP
background paper note that cholesterol-lowering therapy is most
cost-effective when directed toward high-risk populations. The cost of
statins, the most popular class of cholesterol-lowering drugs, is too
high to ignore; the average wholesale price for a year of treatment
with 40 mg/d lovastatin or 20 mg/d simvastatin, exceeds
$1000.26 When used in high-risk men and women, reduced
costs of treating CHD may offset a substantial fraction of these
costs,27 making the drugs highly-cost effective, but the
cost-effectiveness ratio reaches
$1 million per year of life saved
when used in young men or women with very high cholesterol levels but
without other risk factors.3 28 When comparing the
consequences of the NCEP and ACP guidelines, the relevant comparison is
not between treating young adults for high cholesterol and not treating
at all, as is typical for cost-effectiveness analyses. Rather, the
difference is between initiating treatment at, say, age 25 or waiting
until age 35 (or age 45 in women). By delaying of the initiation of
therapy, the ACP guidelines avoid 10 or 20 years of costs and potential
risks while preserving nearly all of the benefit. Seeking and treating
hypercholesterolemia at ages younger than those recommended by the ACP
produce a cost-effectiveness ratio that far exceeds generally accepted
levels.
The ACP guidelines are advisory to physicians, who should exercise judgment and discretionindeed, common sensein applying any set of recommendations to their patients. Physicians are under pressure to handle more problems in increasingly brief office visits and to prioritize the issues and preventive strategies that they will address with each patient. A preventive intervention, even one that begins with something as simple and nominally inexpensive as a cholesterol test, should be recommended only if there is adequate evidence that it is likely to be beneficial. Based on current information, the ACP joined with nearly all major groups applying evidence-based criteria in concluding that cholesterol screening in low-risk young men and women and in asymptomatic older men and women does not meet this standard.
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