Low Framingham Score May Underestimate Coronary Artery Disease Risk Compared With the Presence of Calcium

Emma Hitt, PhD

April 22, 2010

April 22, 2010 — Almost two thirds of women and one fourth of men with substantial atherosclerosis will be missed if subjects are excluded from further screening because they are in the Framingham low-risk category, according to a report published in the May issue of the American Journal of Roentgenology.

"Many coronary events occur in patients without warning, and the need for an effective screening program has been recognized for many years. Historically, the Framingham risk score has been the dominant method of risk stratification in the United States," write study coauthors Kevin M. Johnson, MD, from the Department of Diagnostic Radiology, Yale University School of Medicine, New Haven, Connecticut, and David A. Dowe, from Atlantic Medical Imaging, Galloway, New Jersey.

The researchers sought to compare the sensitivity of the Framingham risk score for extent of atherosclerosis to the sensitivity achieved by the presence or absence of coronary calcium. The reference standard was plaque burden as determined by coronary computed tomography angiography.

A total of 1416 men (mean age, 51.4 years) and 707 women (mean age, 56.9 years), mostly asymptomatic, were included in the analysis. Plaque and stenosis burden were represented by segment plaque score and Duke prognostic score, respectively. Participants with a segment plaque score of 4 or higher or a Duke prognostic score of 3 or higher were considered to have at least a moderate disease burden.

In participants with a segment plaque score of 4 or higher, the presence of any calcium was 98% sensitive in men and 97% sensitive in women. In contrast, a Framingham risk score of 10% or higher was only 74% sensitive in men and 36% sensitive in women. The negative likelihood ratio for the presence of calcium was 0.04 in men and women, whereas the negative likelihood ratio for a Framingham risk score of 10% or lower was 0.38 in men and 0.71 in women.

Similarly, in participants with a Duke prognostic score of 3 or higher, calcium was 97% sensitive in men and 92% sensitive in women, whereas a Framingham risk score of 10% or higher was 88% sensitive in men and 35% sensitive in women. The negative likelihood ratio of calcium presence was 0.05 in men and 0.13 in women, whereas the negative likelihood ratio for a Framingham risk score of 10% or lower was 0.20 in men and 0.75 in women.

"As our study suggests, the presence of coronary artery calcium detects more patients with coronary atherosclerosis than does the Framingham risk assessment score," Dr. Johnson noted in a written release. "If the Framingham risk score is used as the 'gatekeeper' in a screening program for coronary atherosclerosis and the low-risk patients are dismissed from further study, about two thirds of women and a quarter of men with substantial atherosclerosis will be missed."

AJR: Am J Roentgenol. 2010;194:1235-1243.

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