Coronary Artery Calcium Scan: What It Is and Who Needs One

In the U.S., more people die from heart disease than any other condition. The most common type of heart disease is called coronary artery disease (CAD), which is caused by atherosclerosis. This is when plaque builds up in the blood vessels of your heart, restricting blood flow and oxygen to your heart muscle. This can result in heart attacks.

Prevention plays a big role in preventing death from heart disease. And part of that is knowing your risk. A test called coronary artery calcium (CAC) scan can help assess someone's risk for getting heart disease. Let's dive into the details on CAC scans.

What is a coronary artery calcium (CAC) scan?

A coronary artery calcium scan is a high-resolution CT scan that measures calcium in your coronary arteries. Over time, calcium builds up in the walls of our arteries. Plaques can form with the calcium, narrowing the arteries that supply oxygen to our heart, brain, and other organs. This is important because the more calcium and plaque that builds up, the higher the chance of having a stroke or a heart attack.

By looking at the amount of calcium in your coronary arteries - which supply blood and oxygen to the heart muscle - a CAC scan can help estimate your risk. But it's only one tool.

Cardiologists and primary care providers use a CAC scan with other tests and information to determine your risk of cardiovascular disease. This might include a physical exam, lab work, an electrocardiogram (EKG), and your family medical history. Usually these tests are enough to determine someone's risk and what to do about it.

But in some cases, a CAC scan can provide more information. It can help determine whether someone would benefit from starting a medication like a statin. Statins lower your LDL cholesterol and your chances of having a heart attack.

CAC scans can be called other names, such as:

• Coronary calcium score

• Cardiac CT for calcium scoring

• Electron-beam computed tomography (EBCT)

Who should get a CAC?

According to the most recent cholesterol guidelines, CAC testing is only recommended for people with "intermediate" risk of cardiovascular disease. Intermediate risk is defined by a 7.5%-20% risk of having a stroke or heart attack in 10 years, based on other testing.

In more practical terms, someone with an intermediate risk is someone with some risk factors or a family history of heart disease, but with no symptoms. CAC tests help clarify if statin therapy would be beneficial for people with intermediate risk.

The guidelines recommend ordering a CAC test in people who meet the following criteria:

• Adults ages 40 to 75 years

• No history of diabetes mellitus

• LDL cholesterol level between 70 mg/dL and 189 mg/dL

Again, this is because intermediate risk is a bit of a gray area. It's different from situations where statins are definitely recommended: for people older than 40 years with diabetes and/or LDL over 190 mg/dL. These are known risk factors for cardiovascular disease, so experts know that a statin is likely to help these people. They don't need a CAC scan before starting statin medication.

CAC scans are not recommended for:

• People who already have a known heart disease

• People at high risk for coronary artery disease

• Routine screening in people with low risk

• Determining whether treatment is working

What does the coronary artery calcium score mean?

The CAC score is given as a number. The most commonly used scoring system is the Agatston score. It assesses risk as follows:

• 0 = low risk

• 1-100 = minimal to mild risk

• 101-400 = intermediate risk

• 400 or greater = high risk

Calculators such as this one use your CAC score to determine your 10-year heart disease risk.

People with CAC scores of zero have a low chance of developing heart disease, although it may vary by age. The older you are, the more likely a score of zero means you really don't have any coronary artery disease. This might be because plaques get more calcified with age. In other words, younger plaques might not show up as well on a CAC scan.

On the other hand, people with high calcium artery scores (over 400) have a high chance of having a heart attack. But the higher the CAC score, the more imperfect the test is.

So it bears repeating that a CAC scan is rarely used on its own. It's best suited to help you and your primary care provider understand your risk and come up with a treatment plan.

What are the downsides of a CAC test?

One downside of the CAC scan is that it uses radiation. One test likely has minimal consequences, but radiation exposure can add up over a lifetime. A lot of exposure is a risk factor for some cancers.

The other downside to keep in mind is that the CAC scan is not a perfect test. This means it might not accurately predict your risk. A low score indicates low risk, but it's not a guarantee against heart disease. On the other hand, a higher CAC score may result in more testing to see if you really do have coronary artery disease. More invasive testing, such as cardiac catheterization, comes with higher risks, like bleeding.