September 22, 2018
Body scan

Should You Have Your Coronary Calcium Measured?

by Wellness Letter

In January 2018, among the results of President Trump’s medical exam by the White House physician, it was reported that he was one pound shy of being obese, based on his body mass index, and had fairly high LDL (“bad”) cholesterol—143 despite being on a statin drug (below 100 is a commonly accepted goal of treatment). But what caught many people’s attention in the report was that Trump’s coronary artery calcium (CAC) had been measured three times during the past decade. His CAC score is now 133 (considered to be moderate evidence of coronary artery disease—see chart below), up from 98 in 2013 and 34 in 2009. Some medical experts said that his CAC score was even more reason for him to have his cholesterol treated more aggressively, while others countered that it added little to the picture.

If you have elevated cholesterol or just want to get “state of the art” coronary screening, should you also get your CAC measured?

The ABC's of CAC

Deposits of calcium (calcification) can build up in plaques in the walls of arteries that service the heart. This is part of a process called atherosclerosis, which is caused largely by chronic inflammation in blood vessel walls and is an early sign of coronary artery disease. A CAC scan is a quick, noninvasive way to screen for coronary calcium deposits using special computed tomography (CT) scans. CAC results are typically given as an Agatston score, which factors in the area and density of the deposits and ranges from zero to over 400. In theory at least, a CAC score may be a direct measure of total “atherosclerotic burden” and thus “arterial age.”

The value of CAC as a screening test—that is, for people without symptoms, signs, or a history of cardiovascular disease—has been debated for well over a decade now. One uncertainty has been to what extent the test offers useful information for predicting cardiovascular disease beyond what’s provided by an evaluation of standard risk factors, including blood cholesterol levels. The best evidence suggests that CAC testing may be useful for people who are at intermediate coronary riskand thus may be on the fence about treatment, usually a statin.

In new guidelines on testing for “nontraditional” cardiovascular risk factors, the U.S. Preventive Services Task Force concluded that so far there is still insufficient evidence to recommend screening for any of them, including CAC, since it found no definitive clinical research showing that such screening leads to a reduction in cardiovascular events or mortality rates.

Nevertheless, some experts believe that, because of accumulating positive research, CAC testing will be more prominently featured as an adjunct screening option in the update of the influential guidelines for assessing cardiovascular risk and managing blood cholesterol by the American College of Cardiology and the American Heart Association (ACC/AHA) expected in November 2018.

How High Is Your Cardiovascular Risk?

How can you tell if you are at "high" or "intermediate" cardiovascular risk? Here's what the expert groups say.

Clarifying the picture

Doctors have a good idea of what to recommend for patients at low cardiovascular risk (keep up the good work) or high risk (improve lifestyle factors and strongly consider taking a statin). But if you’re one of the tens of millions of Americans who fall in the intermediate-risk category—however that is defined—your choices are not clear-cut.

Standard risk assessment methods are fairly blunt instruments and don’t tell the whole story, especially if you fall in this gray area. A variety of additional tests (besides those for cholesterol, triglycerides, and blood pressure) have been proposed as ways to better predict risk and possibly reclassify intermediate-risk people into the low- or high-risk categories. If you’re clearly at low or high risk, such testing is un­­necessary because the results are very unlikely to change your treatment.

The current ACC/AHA guidelines say that people at intermediate cardiovascular risk may also be candidates for statins. When there’s uncertainty or hesitation about treatment, they suggest that several risk markers be considered, notably family history of premature cardiovascular disease, high blood levels of C-reactive protein (a marker for inflammation), peripheral artery disease (as measured by a test called ankle-brachial index), or elevated CAC.

Though the Task Force did not recommend CAC screening, its systematic re­­search review stated that “overall, CAC appears to be the most promising non­traditional risk factor to add to traditional cardiovascular risk factor assessment.”

The best evidence for the usefulness of CAC screening for people at intermediate risk came from a study in the Journal of the American Medical Association in 2012. It found that CAC testing provided better risk prediction for heart attacks or coronary death, independent of traditional risk factors, than five other nontraditional risk markers (in­­cluding ankle-brachial index, C-reactive protein, and family history of coronary heart disease). During the 7.5-year follow-up, the researchers were able to reclassify 25 percent of intermediate-risk participants to high risk, and another 40 percent to low risk, as a result of their CAC scores. Recently, in a paper in Mayo Clinic Proceedings, researchers from Johns Hopkins University estimated that CAC testing can reclassify (upward or downward) as many as half of all intermediate-risk people. Though the clinical significance of these changes is largely unknown, they should ideally lead to better-informed treatment decisions.

CAC score Presence of coronary artery disease
0 No evidence
1 - 10 Minimal evidence
11 - 100 Mild evidence
100 - 400 Moderate evidence
Over 400 Extensive evidence

Source: RadiologyInfo.org

Zero CAC: a favorable risk factor

Quite a few people have a CAC score of zero (meaning no coronary calcium), which is associated with a very low risk of future cardiovascular events. Scores tend to rise with age. A 2012 study in the European Heart Journal, which included 44,000 asymptomatic people, found a zero CAC score in about half of people ages 45 to 54, one-third of those ages 55 to 64, and one-quarter of those ages 65 to 74. Even 15 percent of those ages 75 to 84 had a zero score.

A common criticism of the ACC/AHA cardiovascular disease risk calculator is that age is such an important factor in it, so that virtually all men over 63 and all women over 70 (even those with no other cardiovascular risk factors) fall above the 10-year threshold for high risk and thus qualify for statin treatment simply by virtue of their age. That may lead to overestimation of risk in relatively healthy people and thus to treatment of many who are unlikely to benefit from it.

A recent study of 4,778 older people (average age 70) without cardiovascular disease, published in JAMA Cardiology, found that 30 percent had a CAC score of zero and that, over an 11-year follow-up, CAC was a better predictor of cardiovascular events than was age. This suggests that many people with a zero CAC score and few cardiovascular risk factors other than age can be reclassified as being at low cardiovascular risk and thus may not need statin treatment. In effect, a zero CAC score would be a strong negative (favorable) risk factor. The researchers called for clinical trials to test this notion.

What to do about high CAC

If a CAC scan reveals calcium deposits, the goal of treatment is to prevent them from progressing, which calls for the standard ways to reduce atherosclerosis, such as in­­tensive dietary changes and loss of excess body weight. The calcified plaques themselves are not the target of treatment because they are actually healed plaques. Rather, the target of treatment is the more dangerous soft plaques, which usually go along with high CAC scores. By the way, cutting down on calcium from food or supplements won’t help; most studies show that there’s no relationship between calcium intake or diet in general and arterial calcification.

Research on the effect of statins (and other cholesterol-lowering medications) on calcification has had conflicting results. Most studies have found little or no effect, or only a slowing of the progression of calcification with high doses. Some research suggests that calcium scores may continue to increase—at least for some time—after initiation of statin treatment, but this may merely represent healing of plaques already present, rather than further progression of atherosclerosis. For that reason, CAC testing may be less meaningful once statins are initiated.

Cautions About Coronary Calcium Testing

If you are considering having your coronary artery calcium (CAC) measured to better assess your cardiovascular risk, you should know its downsides.

Bottom line

If your doctor determines that you are at intermediate cardiovascular risk, you should discuss lifestyle changes—such as quitting smoking or losing excess weight—that may move you into the low-risk category. If that doesn’t help enough and you and your doctor are uncertain about your starting statin therapy, you can discuss the pros and cons of CAC screening as a way to help you decide. It can be part of the shared, individualized decision-making process.

Bear in mind that if you are judged to be at low or high cardiovascular risk, CAC testing wouldn’t serve a purpose.

If you are at intermediate risk and strongly prefer not to start taking a statin or cannot tolerate it, a zero CAC score may justify forgoing (or at least deferring) it, depending on your specific risk factors. On the other hand, discovering that you have significant calcium buildup (CAC over 100) may encourage you and your doctor to more aggressively pursue measures to prevent a heart attack, such as increasing the statin dose or adding another cholesterol-lowering drug, along with renewed efforts at lifestyle improvements.

Final note: Your decision to have the CAC test should be made only after talking with your health care provider. If you decide to undergo testing, make sure the imaging facility is accredited by the American College of Radiology. Steer clear of walk-in clinics that offer CAC testing without a doctor’s prescription, especially as part of a full-body scan.

This article first appeared in the UC Berkeley Wellness Letter.

Also see 13 Tips for Preventing Heart Disease.