If subjects are excluded from further screening because they are in the Framingham low-risk category, almost two-thirds of women and a quarter of men with substantial atherosclerosis will be missed, wrote the authors of a study that appears in the May issue of the American Journal of Roentgenology. “In contrast, the simple observation of any coronary calcium is highly sensitive and moderately specific,” they wrote.
The Framingham Risk Score is often recommended as the starting point for coronary disease screening as an assessment tool is used to estimate a person’s chances of having a heart attack based upon age, sex, total cholesterol, HDL cholesterol, smoking status and blood pressure.
Kevin M. Johnson, MD, from the Yale University School of Medicine in New Haven, Conn., and colleagues compared the sensitivity of the Framingham Risk Score for moderate or greater degrees of atherosclerosis with the sensitivity achieved by simple observation of whether any coronary calcium is present. The reference standard was plaque burden as determined by coronary CT angiography.
Of 1,416 men (mean age, 51.4 years) and 707 women (56.9 years), most were asymptomatic. The researchers estimated plaque burden (segment plaque score) and stenoses burden (Duke prognostic score). A segment plaque score of at least four or a Duke prognostic score of at least three indicated moderate or greater disease burden.
For a segment plaque score of at least four, Johnson and colleagues found the presence of any calcium was 98 percent sensitive in men and 97 percent sensitive in women, whereas a Framingham risk score of at least 10 percent was 74 percent sensitive in men and 36 percent sensitive in women. The negative likelihood ratio for the presence of calcium was 0.04 in subjects of either sex, whereas, for a Framingham risk score of 10 percent or less, the negative likelihood ratio was 0.38 in men and 0.71 in women.
For a Duke prognostic score of at least three, calcium was 97 percent sensitive in men and 92 percent sensitive in women, whereas a Framingham Risk Score of at least 10 percent was 88 percent sensitive in men and 35 percent sensitive in women, according to the authors. 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 percent or less was 0.20 in men and 0.75 in women.
“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,” wrote Johnson and colleagues.
“Our data suggest that, if Framingham Risk Score is used, the cutoff should be set to about 3 percent in men and 1 percent in women to preserve a high sensitivity appropriate for screening,” the authors concluded.