Distribution of C-Reactive Protein Values in the United States
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《新英格兰医药杂志》
To the Editor: Recent studies suggesting that C-reactive protein (CRP) may be an important risk marker for cardiovascular disease have stimulated the demand for testing. Nevertheless, many physicians may be unfamiliar with high-sensitivity CRP measurements. In fact, no description of the distribution of CRP values for the entire adult population (and relevant subgroups) in the United States is readily available to clinicians. We therefore sought to summarize the distribution of CRP for all U.S. adults by age, sex, and race or ethnic background.
We analyzed components of the most recent data released from the National Health and Nutrition Examination Survey (NHANES), 1999 through 2002, which includes a sample of 21,004 people.1 NHANES is conducted by the National Center for Health Statistics, Centers for Disease Control and Prevention, to assess the health and nutritional status of the civilian, noninstitutionalized population of the United States. The complex sampling design, data-collection methods, and weighting approach are described elsewhere.2 We report on the 8874 adults (20 years of age or older) who underwent high-sensitivity CRP testing.
All analyses incorporated four-year sampling weights (WTMEC4YR) to account for the differential probability of selection among subjects and for nonresponse, as well as design-effects variables — the stratum variable (SDMVSTRA) and the variable for the primary sampling unit (SDMVPSU) — in order to account for the survey's complex, multistage sampling strategy. All analyses used the SVY series of commands in the Stata program, version 8.2.
The levels of CRP range from 0.1 to 296.0 mg per liter, with a distribution highly skewed to the right (mean, 4.3; median, 2.1) (Figure 1 and Table 1). The levels of CRP are higher among women than among men (median, 2.7 mg per liter vs. 1.6 mg per liter) and increase with age (median, 1.4 mg per liter among those 20 to 29 years of age vs. 2.7 mg per liter among those 80 years of age or older), but they vary less across categories of race or ethnic background. Recently, researchers have begun to use a CRP level of 2 mg per liter or greater as the threshold for defining high cardiovascular risk.3,4 With use of this threshold, 52 percent of the adult population in the United States would be considered at high risk. The proportion of people with a level of 2 mg per liter or higher is substantial at all ages (e.g., 41 percent among those 20 to 29 years of age vs. 62 percent among those 80 years of age or older).
Figure 1. Distribution and Cumulative Frequency of C-Reactive Protein (CRP) Levels among Women and Men in the United States.
Table 1. Distribution of C-Reactive Protein Levels in the U.S. Population Overall and According to Sex, Age, and Race or Ethnic Group.
These data document that levels of CRP vary with sex and age. Half of U.S. adults have levels greater than 2 mg per liter, highlighting the need for caution in accepting this threshold as the definition of high risk before there is clear evidence of benefit from randomized trials.
Steven Woloshin, M.D.
Lisa M. Schwartz, M.D.
Veterans Affairs Medical Center
White River Junction, VT 05009
steven.woloshin@dartmouth.edu
References
Centers for Disease Control and Prevention. NHANES 2000-1 General data release document. (Accessed March 25, 2005, at http://www.cdc.gov/nchs/about/major/nhanes/nhanes01-02.htm.)
Centers for Disease Control and Prevention. NHANES 2000-1 Analytic guidelines (June 2004). (Accessed March 25, 2005, at http://www.cdc.gov/nchs/about/major/nhanes/nhanes01-02.htm.)
Ridker PM. Rosuvastatin in the primary prevention of cardiovascular disease among patients with low levels of low-density lipoprotein cholesterol and elevated high-sensitivity C-reactive protein: rationale and drug design of the JUPITER trial. Circulation 2003;108:2292-2297.
Ridker PM, Cannon CP, Morrow D, et al. C-reactive protein levels and outcomes after statin therapy. N Engl J Med 2005;352:20-28.
We analyzed components of the most recent data released from the National Health and Nutrition Examination Survey (NHANES), 1999 through 2002, which includes a sample of 21,004 people.1 NHANES is conducted by the National Center for Health Statistics, Centers for Disease Control and Prevention, to assess the health and nutritional status of the civilian, noninstitutionalized population of the United States. The complex sampling design, data-collection methods, and weighting approach are described elsewhere.2 We report on the 8874 adults (20 years of age or older) who underwent high-sensitivity CRP testing.
All analyses incorporated four-year sampling weights (WTMEC4YR) to account for the differential probability of selection among subjects and for nonresponse, as well as design-effects variables — the stratum variable (SDMVSTRA) and the variable for the primary sampling unit (SDMVPSU) — in order to account for the survey's complex, multistage sampling strategy. All analyses used the SVY series of commands in the Stata program, version 8.2.
The levels of CRP range from 0.1 to 296.0 mg per liter, with a distribution highly skewed to the right (mean, 4.3; median, 2.1) (Figure 1 and Table 1). The levels of CRP are higher among women than among men (median, 2.7 mg per liter vs. 1.6 mg per liter) and increase with age (median, 1.4 mg per liter among those 20 to 29 years of age vs. 2.7 mg per liter among those 80 years of age or older), but they vary less across categories of race or ethnic background. Recently, researchers have begun to use a CRP level of 2 mg per liter or greater as the threshold for defining high cardiovascular risk.3,4 With use of this threshold, 52 percent of the adult population in the United States would be considered at high risk. The proportion of people with a level of 2 mg per liter or higher is substantial at all ages (e.g., 41 percent among those 20 to 29 years of age vs. 62 percent among those 80 years of age or older).
Figure 1. Distribution and Cumulative Frequency of C-Reactive Protein (CRP) Levels among Women and Men in the United States.
Table 1. Distribution of C-Reactive Protein Levels in the U.S. Population Overall and According to Sex, Age, and Race or Ethnic Group.
These data document that levels of CRP vary with sex and age. Half of U.S. adults have levels greater than 2 mg per liter, highlighting the need for caution in accepting this threshold as the definition of high risk before there is clear evidence of benefit from randomized trials.
Steven Woloshin, M.D.
Lisa M. Schwartz, M.D.
Veterans Affairs Medical Center
White River Junction, VT 05009
steven.woloshin@dartmouth.edu
References
Centers for Disease Control and Prevention. NHANES 2000-1 General data release document. (Accessed March 25, 2005, at http://www.cdc.gov/nchs/about/major/nhanes/nhanes01-02.htm.)
Centers for Disease Control and Prevention. NHANES 2000-1 Analytic guidelines (June 2004). (Accessed March 25, 2005, at http://www.cdc.gov/nchs/about/major/nhanes/nhanes01-02.htm.)
Ridker PM. Rosuvastatin in the primary prevention of cardiovascular disease among patients with low levels of low-density lipoprotein cholesterol and elevated high-sensitivity C-reactive protein: rationale and drug design of the JUPITER trial. Circulation 2003;108:2292-2297.
Ridker PM, Cannon CP, Morrow D, et al. C-reactive protein levels and outcomes after statin therapy. N Engl J Med 2005;352:20-28.