UCSF

Background

The coronary artery calcium (CAC) score predicts coronary heart disease (CHD) events, but methods for interpreting the score in combination with conventional CHD risk factors have not been established.

Methods and results

We analyzed CAC scores and CHD risk factor measurements from 6757 black, Chinese, Hispanic, and white men and women aged 45 to 84 years in the Multi-Ethnic Study of Atherosclerosis (MESA). CAC was associated with age, sex, race/ethnicity, and all conventional CHD risk factors. Multivariable models using these factors predicted the presence of CAC (C statistic=0.789) and degree of elevation (16% of variation explained) and can be used to update a "pretest" CHD risk estimate, such as the 10-year Framingham Risk Score, that is based on an individual's conventional risk factors. In scenarios in which a high CAC score is expected, a moderately elevated CAC score of 50 is reassuring (eg, reducing risk from 10% to 6% in a healthy older white man), but when a low/zero CAC score is expected, even with identical pretest CHD risk, the same CAC score of 50 may be alarmingly high (eg, increasing risk from 10% to 20% in a middle-aged black woman with multiple risk factors). Both the magnitude and direction of the shift in risk varied markedly with pretest CHD risk and with the pattern of risk factors.

Conclusions

Knowledge of what CAC score to expect for an individual patient, based on their conventional risk factors, may help clinicians decide when to order a CAC test and how to interpret the results.