Implications of C-reactive protein or coronary artery calcium score as an adjunct to global risk assessment for primary prevention of CHD

Background: C-reactive protein (CRP) or coronary artery calcium (CAC) score have been suggested to identify a higher risk subset of intermediate-risk individuals, who potentially could be considered for more aggressive therapy. In the Multi-Ethnic Study of Atherosclerosis (MESA), we estimated the proportion of intermediate-risk participants whose risk status might change based on additional testing using CRP and/or CAC score. Methods: Framingham 10-year CHD risk scores (FRS) were calculated and cross tabulations were used to determine the percent of individuals at intermediate-risk by FRS with a CRP >3 mg/L and/or CAC score >100 AU. Similar analyses were performed using the gender-specific 75th percentile for CRP and CAC. Results: Of the 30% of participants (N = 1450) classified as intermediate-risk by FRS, 30% had a CRP >3 mg/L and 33% had a CAC score >100 AU. Among intermediate-risk women, 49% had a CRP >3 mg/L compared to 27% of intermediate-risk men (p < 0.0001) while the same percent of intermediate-risk women and men (33%) had a CAC score >100 AU. Eleven percent or less of men or women had both a high CRP and CAC score whether conventional or gender-specific cut points were used. When the percent of intermediate-risk individuals with an elevated CRP and/or CAC score in MESA were applied to NHANES III data, over a million intermediate-risk individuals would move to high risk status if CRP or CAC screening directed treatment strategies were uniformly adopted in the U.S. Conclusion: There were differences in the number of intermediate-risk individuals reclassified as high risk depending on the screening test used, the cut points selected, and the demographics of the individuals being screened. These data highlight current limitations of broadly using risk markers such as CRP and CAC score in an intermediate-risk population.