DALLAS, Oct. 1 – Partnering a blood test with an imaging scan may be a better gauge of whether blocked arteries are about to trigger a heart attack or stroke, researchers report in today's rapid access issue of Circulation: Journal of the American Heart Association.
C-reactive protein (CRP) is a marker for inflammation in the blood stream. Calcium deposits in arteries – measured with computerized axial tomography (CAT) scan – indicate the level of plaque buildup. High CRP levels and calcium scores each have been linked with increased heart disease risk, but routine screenings don't test for them. "The exact role of both calcium scores and CRP levels await more definitive studies, but we have found that their combined use is predictive of cardiovascular events," says Robert Detrano, M.D., Ph.D. study coauthor and professor of medicine at UCLA School of Medicine.
The tests are complementary: coronary calcium indicates the presence and amount of coronary atherosclerosis, while CRP suggests that plaque contains inflammatory factors that make it more prone to rupture and block blood vessels.
"Together they can gauge the presence, the amount and the stability of artery-clogging plaque," says Detrano.
Recent research has shown elevated CRP levels impart increased risk of a coronary event, he says. However, it's uncertain whether elevated levels of either cause risk or are just an association.
In Detrano's study, researchers examined data from more than 1,400 people free of heart disease when enrolled. Participants were part of the South Bay Health Watch, a study of adults from Los Angeles suburbs. They were 45 years or older with multiple cardiovascular risk factors, but had not exhibited symptoms of cardiovascular disease. All had their calcium and CRP levels measured. Researchers followed 967 of the people who didn't have diabetes for about six and a half years. People with diabetes were excluded because calcium scores have not been shown to predictive.
Fifty people had a heart attack or cardiovascular death and 104 had a cardiovascular event of some kind in the follow up. These people also had higher calcium scores and CRP levels than people who didn't have a cardiovascular event.
Calcium and CRP levels appeared to be synergistic predictors of cardiovascular events. Researchers noted a six-fold difference in risk of heart attack and cardiac death and a seven-fold difference in the risk of any cardiovascular event between the people at lowest risk compared to people at highest risk.
"Individuals at intermediate risk may benefit from profiling based on high sensitivity CRP levels and coronary calcium, as both factors contribute independently toward the incidence of cardiovascular events," says Detrano.
However, he adds that the findings are not strong enough to back widespread screening.
The research didn't address electron beam computed tomography (EBCT), a popular, but scientifically unvalidated way to measure coronary calcium.