Should I get a Coronary Artery Calcium Test?

The other day a friend of mine asked me if he should get a coronary artery calcium (CAC) test. He is a healthy man in his 40’s without any symptoms of heart problems, but he wants to be proactive about preventing heart disease (the number one cause of death in men and women globally).

Let’s walk through how I would approach this question.

First, what is a CAC? This test is a CT scan that takes less than 10 minutes, does not require contrast, and the radiation exposure is low (similar to that of a mammogram). The test is not covered by insurance and typically costs $100-200. This scan detects calcified plaque in the coronary arteries — a marker of atherosclerosis. Calcium deposits are typically a sign of a chronic plaque that the body has attempted to heal. Having a calcium deposits in your coronary arteries is correlated with having plaque. Unlike risk factors for heart disease, such as smoking or diabetes, this test actually detects disease. It is a screening test intended to detect coronary artery disease in asymptomatic individuals (if you already have heart disease, there is no need for this test).

Here are the possible calcium scores:

It is important to note that this test is not able to identify soft plaque or the amount of stenosis (blockage) in the coronary artery.

So does the CAC score predict coronary artery disease above and beyond what we already know from risk factors, such as cholesterol, hypertension, diabetes, and smoking? Yes it does. As shown in the table below (reference), numerous large studies involving thousands of patients over the past 20 years have shown that CAC is a strong and independent predictor of coronary artery disease and stroke. In addition, this prediction applies regardless of age, gender, and ethnicity.

The American College of Cardiology and American Heart Association for the primary prevention of cardiovascular disease suggests using CAC in those with borderline or intermediate risk (5-7.5% risk of a coronary event in the next 10 years) to further evaluate risk (put your numbers in this risk calculator).

So back to my friend. Now that we know about the CAC test and the supporting evidence behind it, the next question we must ask is, “Would the results change anything we do?” In medicine, before ordering any test it is important to consider if the results would alter the management of the patient.

Let’s say my 45 year old friend has an LDL cholesterol of 130 and is on the fence about taking a medication to lower it. If his CAC comes back at 50, it means he already has plaque in his coronary arteries and he should definitely start taking a statin. In that case, the test would alter the management of this patient.

On the other hand, if my friend was 70 years old and had a CAC of zero, his 10 year risk of a coronary event would be low and he might feel reassured not taking a statin.

I think those two cases above - a young person with an abnormal CAC or an older person with a CAC of zero - are the two scenarios in which the CAC is most useful. In those cases, the result may persuade the first patient to take a statin and reassure the second patient that it may not be necessary.

What if his score was zero? A 45 year old with a CAC of zero is reassuring but it is also expected and age-appropriate. It may give false reassurance that there is no coronary artery disease when in fact there might be still be soft plaque. He might not appreciate that while his 10 year risk of a heart attack is low, with an elevated cholesterol his lifetime risk of a heart attack is nearly 50% (see risk calculator above) even in the absence of any other risk factors.

When I was 40, my LDL was 130 and I was on the fence about taking a statin. My doctor suggested that I get a CAC and if the result was more than zero, to consider taking one. My CAC was zero and I felt reassured. However, after consulting with 2 cardiologists and doing further research, I decided that a lifetime of an LDL of 130 was placing me at increased risk for heart disease. After changes in my diet failed to lower my LDL sufficiently, I started taking a statin. In my case, the CAC score was an unnecessary test - I decided to lower my cholesterol regardless of the result of my CAC test.

I think the CAC test can be useful - particularly if elevated in a younger person or zero in an older person. However, over the years I have become convinced that elevated cholesterol in a younger person should be addressed (lifestyle first, then medications) regardless of the CAC score.

In the case of my 45 year old friend asking about getting a CAC, my reply would be, “What’s your LDL (or ApoB)?” If it’s high, skip the CAC and focus on lowering your cholesterol. I’ll share more on my aggressive approach to cholesterol in my next post.