C-reactive protein (CRP) levels differ by race and gender, which calls into question the use of uniform CRP thresholds for assessing cardiovascular risk. The finding comes from the Dallas Heart Study, a large, multiethnic, population-based sample, and was published in the Journal of the American College of Cardiology (2005;46:464-469).
CRP values higher than 3 mg/L are considered an indicator of increased cardiovascular risk, whereas those less than 1 mg/L are considered to be low risk. These thresholds have been proposed regardless of the patient’s race or gender. The new findings show that blacks have significantly higher CRP levels than whites, and that women have significantly higher levels than men.
“Given the increasing use of CRP as a component of cardiovascular risk in clinical decision-making, our findings have important public health implications,” write the study’s authors.
Amit Khera, MD, MSc, assistant pro-fessor at the University of Texas Southwestern Medical Center in Dallas, and colleagues measured CRP in 2,749 white and black adults aged 18 to 65 years who took part in the Dallas Heart Study, which was designed to study cardiovascular disease. The median CRP level in blacks was 3.0 mg/L compared with a median of 2.3 mg/L in whites (P < .001). The median CRP levels were 3.3 mg/L in women and 1.8 mg/L in men (P < .001).
Black men, black women, and white women all had higher CRP levels compared with white men, with the highest levels observed among black women.
The difference in CRP levels between blacks and whites held even after excluding those subjects who used HMG-CoA reductase inhibitors (statins) or oral estrogen (median levels, 2.6 versus 2.1 mg/L, respectively; P < .001).
Black men, white women, and black women were significantly more likely to have CRP levels higher than 3 mg/L (high risk) than white men. Almost two thirds of the black women in the study had a CRP level greater than 3 mg/L, the authors noted. The differences persisted after excluding statin or oral estrogen users.
“Adjustment for traditional cardiovascular risk factors, body mass index [BMI], statin and estrogen use, and sampling weights attenuated the differences between race and gender groups, yet an elevated CRP level remained more common in white women and black women than in white men (odds ratio [OR] 1.6, 95% confidence interval [CI] 1.1 to 2.5, P < .05; and OR 1.7, 95% CI 1.2 to 2.6, P < .05, respectively),” according to the authors. “In contrast, the differences between black men and white men were no longer statistically significant after multivariate adjustment (OR 1.3, 95% CI 0.8 to 1.9).”
Increasing BMI was associated with higher CRP levels in each race and gender group, but the increase in CRP levels with obesity was greater for women than for men. The greater increase in CRP with increasing BMI in women than in men may explain part of the gender-based differences in CRP levels, they speculate.
Furthermore, “black subjects have a greater prevalence of cardiovascular risk factors than white subjects, and higher CRP levels may reflect this risk factor
burden.” Although racial differences in inflammation may directly contribute
to the higher coronary heart disease
mortality rates in blacks, they add, the possibility also exists that relying on
CRP for risk assessment in blacks may
overestimate cardiovascular event risk in this population, leading to overuse of resources.
“Studies with long-term follow-up will be needed to determine whether these differences in CRP distribution contribute to differences in clinical outcomes and whether CRP risk thresholds should be adjusted for different race and gender groups,” the authors conclude.