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Journal of the American College of Cardiology
© 2000 by the American College of Cardiology
Published by Elsevier Science Inc.
Vol. 36, No. 1, 2000
ISSN 0735-1097/00/$20.00
PII S0735-1097(00)00680-X
Lack of Association of C-Reactive Protein
and Coronary Calcium by Electron Beam
Computed Tomography in Postmenopausal Women:
Implications for Coronary Artery Disease Screening
Rita F. Redberg, MD, MSc, FACC*, Nader Rifai, PhD,† Lauren Gee, MPH,‡
Paul M. Ridker, MD, MPH, FACC§
San Francisco, California, and Boston, Massachusetts
We sought to test the hypothesis that C-reactive protein, a marker of inflammation, would
correlate positively with coronary calcium, a marker of atherosclerosis, in postmenopausal
women.
BACKGROUND High sensitivity testing for C-reactive protein (hsCRP) has recently been shown in large
population studies to predict cardiac events in asymptomatic postmenopausal women.
Coronary calcification determined by electron beam computerized tomography (EBCT) has
also been suggested to be predictive of cardiac events in women.
METHODS
We performed hsCRP testing and determined calcium scores by EBCT in 172 asymptomatic
postmenopausal women (mean age: 64.5 ⫾ 7.9 years) at risk for cardiac disease. Risk factors
were determined by history, physical, electrocardiogram, exercise testing, and lipoprotein
profiles.
RESULTS
Calcium scores ranged from 0 to 2618. For analysis, calcium scores were divided into three
groups; none (0 to 10), minimal (⬎10 to 50), and significant (⬎50). Overall, there was no
significant positive relationship between hsCRP level and calcium score. Specifically, the
hsCRP levels (mg/dl) were 0.24 ⫾ 0.43, 0.33 ⫾ 0.47 and 0.17 ⫾ 0.32 (medians 0.11, 0.15,
and 0.06) for women with none, minimal, and significant coronary calcification, respectively.
In subgroup analysis, a similar lack of positive association was observed after stratification by
smoking status and by hormone replacement therapy use, two factors known to increase
hsCRP.
CONCLUSIONS In contrast to our a priori hypothesis, we found no evidence of a positive association between
hsCRP and calcium score by EBCT. These data thus raise the possibility that hsCRP and
EBCT calcium score reflect different pathologic processes, an issue with implications for
coronary artery disease screening. (J Am Coll Cardiol 2000;36:39 – 43) © 2000 by the
American College of Cardiology
OBJECTIVES
Because lipid screening fails to identify almost half of all
patients at risk for future myocardial infarction (MI), there
is increased interest in nontraditional risk factors and their
role in improving coronary risk prediction (1). One emerging risk factor is C-reactive protein, a sensitive marker for
underlying vascular inflammation, which can be measured
clinically with high sensitivity testing for C-reactive protein
(hsCRP). Several large-scale prospective studies demonstrate that baseline levels of hsCRP predict risk of myocardial infarction, stroke (2,3) and peripheral arterial disease
(4) in apparently healthy men as well as in higher risk
groups such as smokers (5), the elderly (6), those with
angina (7,8) and those with prior MI (9). Similarly, in
asymptomatic postmenopausal women, baseline levels of
From the *Division of Cardiology, University of California, San Francisco,
California; †Department of Pathology, Children’s Hospital Medical Center, Boston,
Massachusetts; ‡Institute for Health Policy Studies, University of California, San
Francisco, California; and §Divisions of Cardiology and Preventive Medicine,
Harvard Medical School, Brigham & Women’s Hospital, Boston, Massachusetts.
These studies were supported by grants from the National Institute of Health: RO1
HL57702 and RO1 HL58755. Dr. Ridker is also supported by an Established
Investigator Award from the American Heart Association, Dallas, Texas.
Manuscript received October 22, 1999; revised manuscript received January 17,
2000, accepted March 2, 2000.
hsCRP are an independent risk factor for future MI, stroke,
revascularization or cardiovascular death (10). Assessment
of hsCRP also appears to add to the predictive value of total
and high density lipoprotein (HDL) cholesterol screening
(11). Thus, it has been hypothesized that hsCRP may
represent either a molecular marker for the extent of
underlying preclinical atherosclerosis, or a marker for rupture prone and unstable plaque.
Calcification of the coronary arteries is also highly correlated with atherosclerosis (12). In this regard, electron beam
computerized tomography (EBCT) is highly sensitive in
detecting coronary calcification and therefore represents a
potential noninvasive screening modality for detection of
subclinical coronary atherosclerosis (13). In contrast to
hsCRP, prospective data evaluating the predictive value of
EBCT are currently limited in asymptomatic populations.
However, one study suggests that coronary calcium may be
predictive of cardiovascular events (14), and it has been
speculated that calcium score by EBCT may be particularly
suitable as a marker of atherosclerosis in women (15),
particularly as other noninvasive modalities, such as stress
testing, are less accurate in women (16).
40
Redberg et al.
C-Reactive Protein and Calcium in Postmenopausal Women
Abbreviations and Acronyms
BMI
⫽ body mass index
CAD
⫽ coronary artery disease
CI
⫽ confidence interval
EBCT ⫽ electron beam computerized tomography
FLASH ⫽ Females, Lipids, Activity and Sex Hormone
Study
HDL
⫽ high density lipoprotein
HRT
⫽ hormone replacement therapy
hsCRP ⫽ high sensitivity testing for C-reactive protein
MI
⫽ myocardial infarction
OR
⫽ odds ratio
Based on these observations, we hypothesized that, because hsCRP levels are consistently associated with increased risk of future coronary events, hsCRP levels would
be significantly higher among women with coronary calcification than among women without calcification. We
tested this hypothesis in a group of asymptomatic postmenopausal women.
METHODS
Subjects. The study population consisted of 172 participants in the Females, Lipids, Activity and Sex Hormone
(FLASH) Study, a cross-sectional evaluation of cardiac risk
factors in women conducted at the University of California
Medical Center (San Francisco), an academic tertiary referral center. Women were recruited by posting flyers in the
community and at local medical practices. Eligible participants were postmenopausal (one-year postmenses) with at
least one additional risk factor for coronary artery disease
(CAD) and without known CAD. All study participants
gave written informed consent. The protocol was approved
by the Committee on Human Research at the University of
California, San Francisco, California.
We assessed cardiac risk factors, hsCRP levels, and
calcium scores by EBCT per research protocol. Age, hormone replacement therapy (HRT), and smoking status were
determined by interview, blood pressure, and body mass
JACC Vol. 36, No. 1, 2000
July 2000:39–43
index (BMI) by examination, lipoprotein values by laboratory testing, and exercise time by treadmill testing. High
sensitivity testing for C-reactive protein was performed
according to the methods described by the manufacturer
(Dade Behring, Newark, Delaware) (17). All EBCT scans
were performed on an Imatron C-150 scanner (South San
Francisco, California) and scored using a previously described protocol (18).
We evaluated the association between levels of hsCRP
and calcium score using the Spearman rank correlation in
the entire group and in subgroups stratified by HRT (19,20)
or smoking status (21), as previous studies have shown CRP
levels to be affected by these factors. Because neither
parameter is normally distributed, we used a proportional
odds model on ordered quintiles of hsCRP and three
ordered categories of calcium (0 to 10 ⫽ “none”; 11 to 50 ⫽
“minimal”; ⬎50 ⫽ “significant”) to assess the strength of the
association, adjusting for age, BMI, smoking status, amount
of exercise, and HRT. We checked for violations of the
proportional odds assumption using the Score test. Differences in the distribution of hsCRP among the three calcium
score groups were assessed with the Kruskal-Wallis test.
Summary results are expressed as mean ⫾ SD, unless
otherwise stated.
RESULTS
Demographics and risk factor profiles for the study participants and subgroups of nonsmokers and non-HRT users
were similar (Table 1). Average Framingham risk score was
14, which would predict a 4% event rate in five years (22).
Overall, no positive relationship was seen between
hsCRP and calcium scores. Specifically, hsCRP levels
(mg/dl) were 0.24 ⫾ 0.43, 0.33 ⫾ 0.47 and 0.17 ⫾ 0.32,
(medians 0.11, 0.15, and 0.06 and ranges 0.02 to 3.10, 0.02
to 1.85, 0.02 to 2.07) for women with none, minimal, and
significant coronary calcification, respectively (Fig. 1).
However, Spearman rank correlation provided no evidence
of a positive association between hsCRP and calcium scores
Table 1. Cardiac Risk Factors
Sample
Age (yrs)
Smokers (%)
Current
Never
Past
HRT users (%)
BMI (kg/m2)
TC (mg/dl)
HDL (mg/dl)
LDL (mg/dl)
Diabetes (%)
FH of CAD (%)
Total
(n ⴝ 172)
Non-HRT Users
(n ⴝ 91)
Noncurrent Smokers
(n ⴝ 161)
64.5 ⫾ 7.9
65.5 ⫾ 8.1
64.6 ⫾ 8.0
5.2
51.2
43.6
47.1
24.4 ⫾ 4.1
256 ⫾ 54
60.5 ⫾ 18.0
164 ⫾ 49
4.7
44.8
2.1
50.5
47.4
—
24.4 ⫾ 4.4
264 ⫾ 59
59.4 ⫾ 1.53
175 ⫾ 54
3.3
44
—
53.4
46.6
46.6
24.3 ⫾ 4.1
256 ⫾ 54
60.9 ⫾ 18.0
165 ⫾ 50
5
44.7
BMI ⫽ body mass index; CAD ⫽ coronary artery disease; FH ⫽ family history; HDL ⫽ high density lipoprotein; HRT ⫽
hormone replacement therapy; LDL ⫽ low density lipoprotein; TC ⫽ total cholesterol.
JACC Vol. 36, No. 1, 2000
July 2000:39–43
Redberg et al.
C-Reactive Protein and Calcium in Postmenopausal Women
41
Figure 1. Box plots illustrating the distribution of levels of C-reactive
protein for women with calcium scores in three groups (0 to 10 ⫽ “none”;
11 to 50 ⫽ “minimal”; ⬎50 ⫽ “significant”). Each box spans the 25th
through 75th percentile; and the median is shown as a horizontal line.
(r ⫽ ⫺0.10, 95%CI [confidence interval] ⫽ ⫺0.25 to 0.05,
p ⫽ 0.18).
Calcium scores ranged from 0 to 2618, with 77 women
(45%) having a calcium score of zero. The average hsCRP in
this zero calcium group was 0.23 mg/liter, compared to
0.24 mg/liter in the women with calcium present (calcium
score ⬎1). In contrast to our a priori hypotheses, we
observed an inverse relationship between CRP quintiles and
calcium scores in proportional odds model. Specifically,
women in the “none” calcium group were 2.0 times more
likely (95% CI 1.1 to 3.7, p ⫽ 0.028), and women in the
“minimal” group were 3.2 times more likely (95% CI 1.4 to
7.4, p ⫽ 0.006) to have higher hsCRP than women with
“significant” calcium. Controlling for risk factors such as
age, smoking status, BMI, exercise time, and HRT increased the strength of this unexpected inverse relationship,
so that adjusted odds ratios [OR] for the “none” and
“minimal” calcium groups were 2.9 (95% CI 1.4 to 5.7, p ⫽
0.003) and 5.0 (95% CI 2.0 to 12.4, p ⬍ 0.001), respectively.
Subgroup analyses among noncurrent smokers and nonHRT users likewise showed no positive association between
hsCRP and calcium scores (Fig. 2), with Spearman rank
correlations of r ⫽ ⫺0.09 for nonsmokers (95% CI ⫽
⫺0.24 to 0.07, p ⫽ 0.27) and r ⫽ ⫺0.047 for non-HRT
users (95% CI ⫺0.25 to 0.61, p ⫽ 0.66), respectively.
DISCUSSION
On an a priori basis, we had hypothesized that women with
EBCT-documented coronary calcium would have significantly higher plasma concentrations of hsCRP than women
without such calcification. However, in this cross-sectional
study of 172 postmenopausal women, we found no evidence
of a positive relationship between hsCRP and calcium
scores. Indeed, if anything, these data suggest an inverse
relationship between hsCRP levels and coronary calcium
Figure 2. Box plots illustrating the distribution of levels of C-reactive
protein for noncurrent smokers (A) and nonhormone replacement therapy
(HRT) users (B) with calcium scores in three groups (0 to 10 ⫽ “none”; 11
to 50 ⫽ “minimal”; ⬎50 ⫽ “significant”). Each box spans the 25th through
75th percentile; and the median is shown as a horizontal line.
measured by EBCT. This possible inverse relationship is
weak and may be due to chance, as the direction of
association is not compatible with the a priori hypothesis
based on proposed biological mechanisms. Nonetheless, we
believe the lack of a positive association between hsCRP
and coronary calcium score deserves careful consideration.
The FLASH participants were similar in demographics
and risk factor profile to the postmenopausal women enrolled in the Women’s Health Study (10) where hsCRP was
shown to be an independent predictor of future cardiovascular events. Thus, these data suggest that the EBCT score,
while a marker for atherosclerotic burden, may not be as
useful as hypothesized in the prediction of actual clinical
events in postmenopausal women. These data also raise the
possibility that hsCRP and EBCT may fundamentally
measure different pathophysiologic processes. In this regard,
hsCRP has been shown to correlate with plasma concentrations of ICAM-1 and IL-6, and thus appears to reflect
the extent of low-grade systemic vascular inflammation.
Recent evidence suggests that plasma concentrations of
IL-6 vary among those with and without a propensity to
42
Redberg et al.
C-Reactive Protein and Calcium in Postmenopausal Women
plaque rupture and subsequent coronary events (23). Thus,
hsCRP, in addition to being a marker for atherosclerotic
burden, may also reflect an underlying propensity to plaque
instability.
In contrast, the lack of correlation in the current data
between EBCT score and hsCRP suggests that calcification
may be less likely to reflect inflammation per se; EBCTdetected calcification may predominantly be a marker for
mature and hence stable atherosclerotic plaque, and thus
only be an indirect marker for the presence of uncalcified
rupture-prone lesions, which may be more likely markers for
future cardiac events.
Deposition of calcium in atherosclerotic lesions has been
shown to be an active process analogous to the formation of
bone spicules (24,25). Furthermore, it appears to involve
cells of special embryonic lineage. Thus, coronary calcification may not merely be a direct consequence of atherogenesis but rather may depend upon the presence of specific
determinants independent of the central processes involved
in plaque formation. Such determinants may be more
directly related to coronary calcium scores than inflammatory markers, which are associated with cardiac events.
In our study, 56% of women had calcium scores close to
or actually at a level of zero while exhibiting a full range of
hsCRP levels, suggesting that there was evidence of underlying vascular inflammation even without coronary calcification. These data may help explain the observation in some
studies that individuals with normal EBCT scores may
nonetheless suffer MI (26). These findings are consistent
with the American Heart Association Writing Group’s
Scientific Statement, which found that only a small proportion of individuals with atherosclerosis and detectable coronary calcium will develop clinical coronary events (13). Our
observation also supports the possibility that these markers
detect different components of the atherothrombotic process. Furthermore, these data are consistent with the observation that hsCRP predicts future vascular risk in subgroups
of women who otherwise appear to be at low coronary risk
by traditional methods for risk detection (10).
Study limitations. There are several limitations to our
study. The sample size is modest and we had relatively few
women with high calcium scores. However, in these data,
the power to detect a difference in hsCRP levels across
calcium score groups is nonetheless high. Further, because
the negative predictive value of EBCT is critical to evaluating its utility as a screening method, we believe our
population to be an appropriate cohort for this analysis.
However, as our data came from women without known
coronary events, generalizing to a secondary prevention
setting or to men must be done with caution. Second, our
data are cross-sectional and thus cannot determine whether
hsCRP or EBCT scores predict event rates. However,
women in the FLASH study were similar to those in the
Women’s Health Study where hsCRP did provide a strong
independent marker of risk for future cardiovascular events.
In contrast, Secci and colleagues (27) have reported that
JACC Vol. 36, No. 1, 2000
July 2000:39–43
calcium score is a weak predictor of coronary death and
infarction, but is most accurate for predicting revascularization procedures. Understandably, as most studies of EBCT
to date have been unblinded, it is difficult to assess whether
the predictive value of EBCT for revascularization reflects
progression of underlying atherosclerosis or physician bias.
Recent data from a study of asymptomatic high-risk men
with 41-month follow-up found that calcium score by
EBCT did not accurately predict cardiac events (28).
In sum, this cross-sectional study found no evidence of a
positive association between hsCRP and coronary calcification as detected by EBCT, despite the fact that large-scale
prospective studies have demonstrated that hsCRP predicts
risk of future coronary events. These data highlight the
importance of careful prospective clinical evaluation of
emerging technologies such as EBCT in the detection of
coronary disease. Such studies, if performed in a blinded
fashion such that physician and patient interventions are not
biased by knowledge of EBCT score, will provide a critical
evaluation of this imaging technology.
Reprint requests and correspondence: Dr. Rita F. Redberg,
The Division of Cardiology, University of California, San Francisco, 505 Parnassus Avenue, San Francisco, California 941430124. E-mail: [email protected].
REFERENCES
1. Ridker PM. Evaluating novel cardiovascular risk factors; can we better
predict heart attacks? Ann Intern Med 1999;130:933–7.
2. Ridker PM, Cushman M, Stampfer MJ, et al. Inflammation, aspirin,
and the risk of cardiovascular disease in apparently healthy men.
N Engl J Med 1997;336:973–9.
3. Koenig W, Sund M, Fröhlich M, et al. C-Reactive protein, a sensitive
marker of inflammation, predicts future risk of coronary heart disease
in initially healthy middle-aged men: results from the MONICA
(Monitoring Trends and Determinants in Cardiovascular Disease)
Augsburg Cohort Study, 1984 to 1992. Circulation 1999;99:237– 42.
4. Ridker PM, Cushman M, Stampfer MJ, et al. Plasma concentration of
C-reactive protein and risk of developing peripheral vascular disease
(see comments). Circulation 1998;97:425– 8.
5. Kuller LH, Tracy RP, Shaten J, et al. Relation of C-reactive protein
and coronary heart disease in the MRFIT nested case-control study.
Multiple Risk Factor Intervention Trial. Am J Epidemiol 1996;144:
537– 47.
6. Tracy RP, Lemaitre RN, Psaty BM, et al. Relationship of C-reactive
protein to risk of cardiovascular disease in the elderly. Results from the
Cardiovascular Health Study and the Rural Health Promotion Project.
Arterioscler Thromb Vasc Biol 1997;17:1121–7.
7. Liuzzo G, Biasucci LM, Gallimore JR, et al. The prognostic value of
C-reactive protein and serum amyloid A protein in severe unstable
angina. N Engl J Med 1994;331:417–24.
8. Haverkate F, Thompson SG, Pyke SD, et al. Production of C-reactive
protein and risk of coronary events in stable and unstable angina.
European Concerted Action on Thrombosis and Disabilities Angina
Pectoris Study Group. Lancet 1997;349:462– 6.
9. Ridker PM, Rifai N, Pfeffer MA, et al. Inflammation, pravastatin, and
the risk of coronary events after myocardial infarction in patients with
average cholesterol levels. Cholesterol and Recurrent Events (CARE)
Investigators. Circulation 1998;98:839 – 44.
10. Ridker PM, Buring JE, Shih J, et al. Prospective study of C-reactive
protein and the risk of future cardiovascular events among apparently
healthy women. Circulation 1998;98:731–3.
11. Ridker PM, Glynn RJ, Hennekens CH. C-reactive protein adds to the
JACC Vol. 36, No. 1, 2000
July 2000:39–43
12.
13.
14.
15.
16.
17.
18.
19.
20.
predictive value of total and HDL cholesterol in determining risk of
first myocardial infarction. Circulation 1998;97:2007–11.
Blankenhorn D. Coronary arterial calcification: a review. Am J Med
Sci 1961;2424:41–9.
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;94:1175–92.
Arad Y, Spadaro LA, Goodman K, et al. Predictive value of electron
beam computed tomography of the coronary arteries. 19-month
follow-up of 1173 asymptomatic subjects. Circulation 1996;93:
1951–3.
Janowitz WR, Agatston AS, Kaplan G, et al. Differences in prevalence
and extent of coronary artery calcium detected by ultrafast computed
tomography in asymptomatic men and women. Am J Cardiol 1993;
72:247–54.
Kwok Y, Kim C, Grady D, et al. Meta-analysis of exercise testing to
detect coronary artery disease in women. Am J Cardiol 1999;83:
660 – 6.
Rifai N, Tracy RP, Ridker PM. Clinical efficacy of an automated
high-sensitivity C-reactive protein assay. Clin Chem 1999;45:2136 –
41.
Agatston AS, Janowitz WR, Hildner FJ, et al. Quantification of
coronary artery calcium using ultrafast computed tomography. J Am
Coll Cardiol 1990;15:827–32.
Cushman M, Meilahn E, Psaty B, et al. Hormone replacement
therapy, inflammation, and hemostasis in elderly women. Arterioscler
Thromb Vasc Biol 1999;19:893–9.
Ridker PM, Hennekens CH, Rifai N, et al. Hormone replacement
Redberg et al.
C-Reactive Protein and Calcium in Postmenopausal Women
21.
22.
23.
24.
25.
26.
27.
28.
43
therapy and increased plasma concentration of C-reactive protein.
Circulation 1999;100:713– 6.
Tracy RP, Psaty BM, Macy E, et al. Lifetime smoking exposure affects
the association of C-reactive protein with cardiovascular disease risk
factors and subclinical disease in healthy elderly subjects. Arterioscler
Thromb Vasc Biol 1997;17:2167–76.
Anderson KM, Wilson PW, Odell PM, et al. An updated coronary
risk profile. A statement for health professionals. Circulation 1991;83:
356 – 62.
Biasucci LM, Vitelli A, Liuzzo G, et al. Elevated levels of
interleukin-6 in unstable angina. Circulation 1996;94:874 –7.
Parhami F, Demer LL. Arterial calcification in face of osteoporosis in
ageing: can we blame oxidized lipids? Curr Opin Lipidol 1997;8:
312– 4.
Parhami F, Morrow AD, Balucan J, et al. Lipid oxidation products
have opposite effects on calcifying vascular cell and bone cell differentiation. A possible explanation for the paradox of arterial calcification
in osteoporotic patients. Arterioscler Thromb Vasc Biol 1997;17:
680 –7.
Detrano RC, Wong ND, Tang W, et al. Prognostic significance of
cardiac cinefluoroscopy for coronary calcific deposits in asymptomatic
high risk subjects. J Am Coll Cardiol 1994;24:354 – 8.
Secci A, Wong N, Tang W, et al. Electron beam computed tomographic coronary calcium as a predictor of coronary events: comparison
of two protocols. Circulation 1997;96:1122–9.
Detrano RC, Wong ND, Doherty TM, et al. Coronary calcium does
not accurately predict near-term future coronary events in high-risk
adults (see comments). Circulation 1999;99:2633– 8.