A painless imaging test can let your doctor peek right into your arteries to see if dangerous plaque deposits (atherosclerosis) are putting you at risk for heart disease before you have any signs or symptoms. Here’s what you need to know about the coronary artery calcium (CAC) test and if you’re a candidate for it.

What is the CAC test?

The CAC test is a type of CT scan. Using rapid X-rays, it takes cross-­sectional images of the blood vessels that supply your heart. A radiologist or technician places electrodes on your chest to monitor your heart activity and takes images between heartbeats. You just need to hold your breath and lie still for the few seconds it takes to capture each image. There are no preparatory or post-activity restrictions; it’s non-invasive and painless; and it takes only a few minutes once you’re on the exam table.

Your doctor can then look at the images for specks of calcium on the blood vessel walls. (The plaque that deposits on blood vessel walls includes cholesterol and calcium.) Your doctor will count the calcium specks to determine your score and use that number to extrapolate the degree of plaque buildup. (Coronary artery calcium is not the same calcium that’s in your bones, and it’s not a reflection of the amount of calcium in your diet.)

What does your CAC score mean?

A higher CAC score means there is more plaque along the artery walls and you have a greater risk of a heart attack. Here’s how the numbers break down:

  • Zero. No calcium was detected. You have a low heart attack risk, but if you have a strong family history of atherosclerotic cardiovascular disease (ASCVD), smoke, or have type 2 diabetes, you may be advised to start a cholesterol-lowering drug like a statin.
  • One to 99. Calcium is starting to accumulate. If you have other cardiovascular risk factors, your doctor may discuss risk-reduction options, including cholesterol-lowering therapy.
  • 100 to 300. You have a moderate amount of plaque deposits and an elevated risk of a heart attack or stroke over the next five to 10 years. Most people in this range need to start on a statin.
  • 300 or higher. This is a sign of very high to severe atherosclerosis and heart attack risk.

Your score will be compared to findings in other men or women in your age group. The average white man will get a nonzero score by age 53. For the average white woman, it’s age 62. These stats are similar for people of Asian descent. For African Americans, nonzero scores happen a few years later. If you develop plaque ahead of your peer group, you may need to fast-track treatment.

Though your CAC score isn’t the only factor to consider for heart attack prevention, it will inform decision-making about treatments to stop plaque progression and other steps to help prevent heart attack and stroke. These might include following a better diet, getting more exercise, losing weight, and taking medications.

Who benefits most from the test?

The CAC test isn’t recommended for everyone. It is most helpful for people whose heart attack risk falls in an intermediate zone based on, in part, the score on an atherosclerotic cardiovascular disease (ASCVD) screening tool. The ASCVD evaluates numbers like cholesterol levels and blood pressure readings to determine how likely you are to have a heart attack in 10 years. (You can take the test yourself online at (https://tools.acc.org).

The CAC test isn’t for people who have a 5 percent or lower 10-year heart attack risk and no strong family history of heart disease, because the odds of finding calcium are low. It also isn’t deemed necessary for people with a 10-year risk of 20 percent or higher, because it’s almost a given that they will have plaque. It makes the most sense for people who have between a 5 and 20 percent risk: Half of people in this group will have calcium deposits and half won’t.

Compared with the traditional and imperfect approach of estimating heart disease via risk factors like blood pressure and cholesterol levels, the CAC test directly answers the question of whether you have atherosclerosis. That’s why it’s so powerful. Since it can also tell if there are no calcium deposits, the result can be reassuring for someone with moderate heart disease risk factors.

The chief drawback to the test is that it may not be covered by your insurance, so it could cost between $100 and $400. The radiation exposure is similar to a mammogram and having the test at a facility with the most up-to-date technology means you’ll get the lowest amount of radiation possible.

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