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High-Sensitivity C-Reactive Protein: A Useful Marker for Cardiovascular Disease Risk Prediction and the Metabolic Syndrome

Posted on: Saturday, 5 March 2005, 03:00 CST

Every year, 1.3 million Americans suffer a myocardial infarction with only one half of them exhibiting evidence of dyslipidemia. The identification of additional risk factors for cardiovascular disease is therefore of paramount importance. Of the examined novel biochemical markers, high-sensitivity C-reactive protein (hs-CRP) is the most promising. To date, 22 prospective epidemiologic studies have demonstrated that hs-CRP is a strong predictor of future vascular disease, 6 cohort studies have shown that hs-CRP measurements add prognostic value beyond that available from the Framingham risk score, and 8 cohort studies have confirmed that hs- CRP adds prognostic information in the metabolic syndrome and in the prediction of type 2 diabetes (1). These studies, done by various groups in Europe and the United States, examined middle-aged and elderly men and women, and some included different ethnic and racial groups. As a result of these findings and the fact that hs-CRP can be reliably and accurately measured by clinical laboratories, the American Heart Association (AHA) and the CDC issued joint guidelines about the implementation of hs-CRP measurement as part of the global risk assessment of cardiovascular disease (2).

In this Journal, Levinson et al. (3) recently questioned the validity of using hs-CRP to predict future cardiovascular disease. These authors relied in their argument on data from the Women's Health Study (WHS) (4) and the recently published article from the Reykjavik Study by Danesh et al. (5). We would like to point out some of the important issues regarding these two studies.

Using the WHS cohort, we directly compared the ability of hs-CRP and LDE-cholesterol to predict future coronary events in 27 939 participants over a follow-up period of 8 years (4). Our data clearly showed that hs-CRP was superior to LDL-cholesterol in its ability to predict risk (fully adjusted relative risks, 2.3 for hs- CRP and 1.5 for LDL-cholesterol; both P <0.001). In addition, we demonstrated that hs-CRP provided additional prognostic information at all LDL-cholesterol concentrations and Framingham risk scores. After adjustment for all components of the Framingham risk score, hs- CRP remained a strong predictor of future risk. It is surprising that Levinson et al. (3), using these data, questioned the ability of hs-CRP, but not LDL-cholesterol, to predict future cardiovascular disease risk.

We also examined 3597 of those women who have metabolic syndrome, as defined by the National Cholesterol Education Program, and have been followed for 8 years for first-ever cardiovascular events (6). The probability of cardiovascular event-free survival in these women was markedly affected by their hs-CRP values (Fig. 1). Baseline hs- CRP concentration was able to differentiate between low, moderate, and high risk of future cardiovascular events among those with metabolic syndrome, indicating the clinical benefit from its measurement in this patient population. Clearly, more aggressive interventional measures are warranted for those patients with increased hs-CRP.

Fig. 1. Clinical predictive value of hs-CRP at three cut points in individuals with metabolic syndrome.

In the article by Danesh et al. (5), hs-CRP was measured in baseline samples from 2459 patients who developed a nonfatal myocardial infarction or died from coronary heart disease during a follow-up period of >30 years and in 3969 controls without coronary events. The authors concluded that hs-CRP is a moderate predictor of coronary heart disease risk and that the recommendation for its use should be revisited. However, these conclusions are not consistent with the presented data. The authors used the cutoff point of 2 mg/ L rather than the 3 mg/L recommended by the AHA/CDC guidelines (2) and therefore may have underestimated the risk associated with hs- CRP. In addition, they adjusted not only for the Framingham risk score but also for diabetes, triglycerides, obesity, pulmonary function, social status, and other inflammatory markers that tend to reduce the predictive ability of hs-CRP. Even in this conservative analysis and estimation of increment in risk, an odds ratio for hs- CRP of 1.5 (a 50% increase in risk) is a significant finding from a clinical and a public health perspective (7).

We reanalyzed our data from the WHS, using the cut points used by Danesh et al. (5). The odds ratios in both studies were almost identical for hs-CRP at a cut point of 2 mg/L, highest vs lowest quintile, and the 10-year risk estimate (Table 1). These odds ratios are also similar to those reported in the Monitoring Trends and Determinants in Cardiovascular Disease (MONICA) and the Atherosclerosis Risk in Communities (ARIC) studies (8). Furthermore, cholesterol concentrations in Iceland in 1967 were much higher than the current ones in the United States and could have contributed to the increased risk associated with cholesterol and the reduced risk associated with hs-CRP seen in that report (8). In addition, the odds ratios and the areas under the ROC curves were almost identical for hs-CRP, cigarette smoking, and hypertension. Therefore, if the authors of that report and Levinson et al. (3 ) doubt the ability of hs-CRP to predict future cardiovascular events, they must also believe that cigarette smoking and hypertension are unimportant risk factors.

Table 1. Comparison between the Reykjavik and the WHS risk predictions.

In summary, we find the arguments and conclusions reached by Levinson et al. (3) to be misleading because they are not supported by scientific evidence. However, we agree with Lriem that investigators from the major prospective studies, epidemiologists, cardiologists, and laboratorians should together reexamine current guidelines because a tremendous amount of data has become available since the AHA/CDC expert panel was convened in March 2002. We believe that the consistency of the data will lead to a further widening of the use of hs-CRP as a clinical criterion for metabolic syndrome and as part of a modified cardiovascular risk score useful for global risk assessment in both men and women.

References

1. Ridker PM, Wilson PW, Grundy SM. Should C-reactive protein be added to metabolic syndrome and to assessment of global cardiovascular risk? Circulation 2004;109:2818-25.

2. Pearson TA, Mensah GA, Alexander RW, Anderson JL, Cannon RO 3rd, Criqui M, et al. Markers of inflammation and cardiovascular disease: application to clinical and public health practice: a statement for healthcare professionals from the Centers for Disease Control and Prevention and the American Heart Association. Circulation 2003;107:499-511.

3. Levinson SS, Miller JJ, Elin RJ. Poor predictive value of high- sensitivity C-reactive protein indicates need for reassessment. Clin Chem 2004;50: 1733-5.

4. Ridker PM, Rifai N, Rose L, Buring JE, Cook NR. Comparison of C-reactive protein and low-density lipoprotein cholesterol levels in the prediction of first cardiovascular events. N Engl J Med 2002;347:1557-65.

5. Danesh J, Wheeler JG, Hirschfield GM, Eda S, Eiriksdottir G, Rumley A, et al. C-Reactive protein and other circulating markers of inflammation in the prediction of coronary heart disease. N Engl J Med 2004;350:1387-97.

6. Ridker PM, Buring JE, Cook NR, Rifai N. C-Reactive protein, the metabolic syndrome, and risk of incident cardiovascular events: an 8-year follow-up of 14 719 initially healthy American women. Circulation 2003;107:391-7.

7. Foody JM, Gotto AM, Wenger N. C-Reactive protein and coronary heart disease. N Engl J Med 2004;351:295-8; author reply, 295-8.

8. Ridker PM, Koenig W, Fuster V. C-Reactive protein and coronary heart disease. N Engl J Med 2004;351:295-8; author reply, 295-8.

Nader Rifai

Children's Hospital

and

Harvard Medical School

Boston, MA

Address for correspondence: Children's Hospital, Department of Laboratory Medicine, 300 Longwood Ave., Boston, MA 02115. Fax 617- 730-0383; Nader.rifai@tch.harvard.edu.

DOI: 10.1373/clinchem.2004.044990

Copyright American Association for Clinical Chemistry Mar 2005

Source: Clinical Chemistry

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