GRUNDY
ET AL., Assessment of Cardiovascular Risk
J Am Coll Cardiol 1999;34:1348--59
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
VII.
Relative Risk Versus Absolute Risk: Estimations From
Framingham Scores
The
relative risk is the ratio of the absolute risk of a given
patient (or group) to that of a low-risk group. Literally,
the term relative risk represents the ratio of the incidence
in the exposed population divided by the incidence in
unexposed persons. The denominator of the ratio can be
either the average risk of the entire population or the
risk of a group devoid of risk factors. The Framingham
definition of the low-risk state provides a useful denominator
to determine the effect of risk factors on a patient's
risk. Both the absolute and relative risk can be derived
from the recently published risk score sheets.2
The
first step in estimating risk is to calculate the number
of Framingham points for each risk factor(Table
4). For initial assessment, measurements of serum
levels of total cholesterol (or LDL-C) and HDL-C are
required.2
The points for total cholesterol instead of LDL-C are
listed in Table 4 because
some of the Framingham database did not include LDL-C.
Hence, total cholesterol gives more robust estimates.
Evaluation for cholesterol disorders requires measurement
of LDL-C, which is also the primary target of cholesterol-lowering
therapy.6
The blood pressure value used in scoring is that obtained
at the time of assessment, regardless of whether the
patient is taking antihypertensive drugs. The average
of several blood pressure measurements is needed for
an accurate determination of the baseline level. Finally,
in the present report, Framingham risk scores for borderline
elevations have been modified to assign stepwise incremental
risk in accord with current NCEP6
and JNC VI7
guidelines. Failure of Framingham scores to identify
stepwise increments in risk in borderline zones probably
reflects the relatively small size of the Framingham
cohort. Diabetes is defined as a fasting plasma glucose
level <126 mg/dL, to conform with recent ADA guidelines;18
in the Framingham study, diabetes was defined as a fasting
glucose level >140 mg/dL. The designation of "smoker"
indicates any smoking in the past month. The total risk
score sums the points for each risk factor.
Risk
ratios, relative to the low-risk state(Table
3), are shown for men in Figure
1 and for women in Figure 2;
for each age, the number shown gives the relative risk.
In addition, 10-year absolute risk values are shown
for both total and hard CHD. The definition of hard
CHD is that used by Framingham investigators; values
shown for hard CHD are approximately two thirds those
for total CHD, which are in accord with the recent Framingham
report.2
Gradations of increasing relative risk are given in
color. At the midpoint of this gradation is the average
risk for the Framingham cohort for each age range. Ratios
above average are divided into moderately high relative
risk and high relative risk. A 3-fold increase in relative
risk above the lowest risk level is designated moderately
high risk; a 4-fold or greater increase is called high
risk. Absolute risk levels rise progressively with age,
even in the absence of risk factors.
Relative
risk is useful for providing the physician with an immediate
perspective of a patient's overall risk status relative
to a low-risk state. This perspective can be helpful
as a frame of reference for both physician and patient.
Moreover, relative risk probably can be used to compare
risk among individuals in populations in which baseline
absolute risk has not been established. Absolute baseline
risk (low-risk level) almost certainly varies among
different populations, but the relative contributions
of individual risk factors to total risk appear to be
similar among all populations. Although the comparability
of relative risk has not been proven rigorously, examination
of available data from different epidemiological studies19–28
suggests this to be the case.
It
is apparent from Figures 1 and
2 that the relative risk associated
with a given set of risk factor levels (expressed as
a single Framingham number) declines with advancing
age. At the same time, 10-year absolute risk rises with
aging. Both changes have implications for prevention.
Higher relative risk estimates in young adults are an
indication of the high long-term risk accompanying the
risk factors; they point to the need to institute a
long-term risk-reduction strategy. On the other hand,
the increasing absolute risk that accompanies advancing
age reveals the opportunity for reducing absolute short-term
risk by an immediate aggressive reduction of risk factors
in older people. However, the best candidates for aggressive
risk reduction among older patients may be those with
moderately high or high relative risk. Recent guidelines
have emphasized absolute risk estimates for use in treatment
guidelines. Even so, the utility of relative risk estimates
for areas of primary prevention that are most contentious,
specifically, in young adults and elderly patients,
should not be overlooked in the development of future
guidelines.
Copyright
© 2000 by The American Heart Association, Inc.
and
The American College of Cardiology
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