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Coronary Calcium Score (Coronary Artery Calcification): Nuts and Bolts

November 7, 2020 | Dr Reza Moazzeni

Table of Contents

Coronary Artery Calcium, or CAC score, is a valuable test for estimating the future risk of a heart attack. In this comprehensive guide, I will discuss the advantages and disadvantages of this test and how it can be helpful when ordered appropriately or harmful if requested and interpreted incorrectly.

Video: This video illustrates the importance of Coronary Calcium Score, when to consider and how to interpret the results.

Understanding the ASCVD (AtheroSclerotic CardioVascular Disease) Risks and ASCVD risk calculation

For decades, investigators have been trying to discover the “risk factors” that increase the likelihood of heart attack. They have identified many such factors through years of intensive and elegant research, including age, sex, smoking habits, obesity, a sedentary lifestyle, high blood pressure (hypertension), positive family history of heart attack, menopause, inflammatory diseases like rheumatoid arthritis, high cholesterol levels (hypercholesterolemia) and last but not least, diabetes. Numerous studies have proven that we can significantly reduce the risk of a heart attack by modifying these factors, also known as “traditional risk factors”.

ASCVD risk calculation:

To estimate an individual’s risk of heart disease in the next decade, we input these risk factors into a calculator, such as the ASCVD risk estimator plus. It is important to note that we use this calculator solely for primary prevention. It’s not for those with a history of heart attack, stent, bypass surgery, or known coronary artery disease based on imaging.

Interpreting the results:

The ASCVD calculator categorizes individuals into three groups based on their risk level for developing cardiovascular disease in the next ten years: low-risk, intermediate-risk, and high-risk. If your risk level falls under the low-risk category, your risk of developing cardiovascular disease is less than 5%. Individuals who fall under the intermediate-risk category have a risk factor ranging from 5% to 19%, while those who fall in the high-risk group have a risk of 20%.

10-year risk of heart attack

Limitations of Online Risk Calculators

Despite these advancements, many individuals still suffer from a heart attack prematurely without having any or only a few of these risk factors. This suggests that our current risk calculators, developed based on “traditional risk factors,” are not optimal and can potentially miss many “preventable” cases of heart attack.

To overcome these shortcomings, we constantly search for additional risk factors that could improve the accuracy of our heart attack risk predictions. In the past 20 years, two factors have emerged as significant predictors of such events: coronary calcium score (CAC score) and Lipoprotein a or Lp(a). In this post, I will discuss the coronary calcium score.

High cholesterol levels (Hypercholesterolemia), familial (FH) or non-familial, is a significant risk for early-onset coronary artery disease and atherosclerosis.

If you have high LDL-cholesterol levels, particularly at a young age, utilizing an “online FH calculator” can provide valuable insights into whether your hypercholesterolemia is genetically inherited. To learn more about hypercholesterolemia, check our article about Familial Hypercholesterolemia and the stepwise approach to a case of severe hyperlipidemia.

What is the Coronary Calcium Score (Heart Calcium Test)?

Coronary plaques are known to be the primary precursors of myocardial infarction. The driver behind plaque formation in the arterial wall is Atherosclerosis, an inflammatory process that typically starts at a young age. Based on the presence or absence of calcium, plaques are classified into “soft” or “calcified”. Initially, they are soft and have no detectable calcium, but calcification accelerates within the plaques as we age.

X-ray images such as a CT scan can readily identify these calcified spots. A coronary calcium score is a noninvasive CT scan that measures the amount of calcium deposited in the calcified plaques in the coronary arteries. It quantifies calcium deposits and calculates a score. Evidence has shown that the higher the score, the higher the risk of future cardiac events and stroke.

Figure 1: This CT scan, which belongs to a 60-year-old asymptomatic man, shows significant calcification of the LAD and RCA arteries. It implies that beneath this buildup of calcium, the process of “atherosclerosis” is progressing rapidly. If left uncontrolled, this can result in acute coronary syndromes (heart attack).

He was initially labeled as “low-risk” based on traditional risk factor calculations. However, this single new finding (high coronary calcium score) will change his previous “low-risk” status to “high-risk.”

Who should have a CAC test?

It is crucial to understand that the CAC test is not appropriate for everyone. 

The CAC test is generally recommended for the following groups of individuals:

    • Asymptomatic adults with low to intermediate risk of cardiovascular disease based on traditional risk factors.
    • Asymptomatic adults with borderline or unclear risk factors, where the CAC score can help guide preventive therapy decisions such as starting medical therapy for hypercholesterolemia.

The CAC test is not recommended for the following groups:

    • High-risk individuals: Those classified as high-risk based on the ASCVD risk calculator (10-year risk >20%) should not undergo a CAC test. Regardless of the score, these individuals require intensive medical therapy, lifestyle modifications, and management of their risk factors.
    • Symptomatic patients: Individuals presenting with symptoms suggestive of coronary artery disease, such as chest pain or shortness of breath, should not have a CAC test. In these cases, diagnostic tests like CT coronary angiogram or stress echocardiogram are appropriate to evaluate the cause of the symptoms.
    • Very low-risk individuals: In those with no risk factors and a very low likelihood of developing cardiovascular disease, the CAC test may not provide additional benefit and is generally not recommended.

To illustrate how the CAC score check can be helpful, here I present a typical case:

A 55-year-old man presents after his close friend suffered a massive myocardial infarction. They have been colleagues and used to exercise regularly, engaging in weekly swimming, cycling, and running. He does not smoke, eats a healthy diet, and has no significant family history of ischemic heart disease. His cholesterol levels are borderline, and he has mild hypertension, which is well-controlled medically. He is not complaining of any symptoms indicative of angina. He insists that his friend had the same profile and was at low risk for myocardial infarction. He prefers not to take any other medications.

In this scenario, a coronary calcium score provides valuable information to further assess his future risk of ischemic heart disease. He underwent a calcium score test, which was 300. A calcium score at this level will immediately move him from the low-risk to moderate-to-high-risk categories. He would benefit from intensive medical therapy, aiming for an LDL-Cholesterol between 1.4-1.6 mmol/L (convert to mg/dl) and likely Aspirin.

This case reiterates that coronary calcium scoring should only be considered in individuals with "low to intermediate" baseline risk. A high coronary calcium score can modify someone's low-risk status to high-risk, prompting more aggressive preventive measures and lifestyle changes. However, it is essential to remember that the reverse is not true; a low or even zero calcium score does not change the status of a high-risk patient to a low-risk.

A “high-risk” individual will remain “high-risk” regardless of their calcium score. They should receive intensive medical therapy and be encouraged to follow a healthy lifestyle.

When to consider checking your calcium score?

Coronary Calcium test should be considered in individuals between 45-70 years of age. This does not mean those below 45 or above 70 cannot undergo the test, but we should interpret the results cautiously. As mentioned before, the CAC test only detects plaques that contain calcium, and it misses soft plaques that do not have calcium. 

Coronary calcium score below 45

In those under 45, there has not been enough time for the lipid-rich soft plaques to calcify, and the test can miss them. For example, a 30-year-old patient with familial hypercholesterolemia could have many soft (non-calcified) coronary plaques. This individual’s CAC score will be zero, as no calcium has yet formed within the plaques, while his risk of cardiac events is significantly elevated. In such cases, a CAC score of 0 can be misleading, resulting in false reassurance and leniency towards treatment. On the contrary, a high calcium score in a young patient is highly concerning and should be taken seriously, as it indicates that they have already formed coronary plaques with an increased risk of future ischemic heart disease (IHD).

Coronary calcium score above 70 

Nearly everyone has some degree of coronary artery calcification above 70. A high calcium score in older people does not necessarily indicate high-risk status unless significantly elevated. However, a low or zero calcium score in this age group can be extremely reassuring.

Rather than focusing on the calcium score’s absolute number, it is essential to compare your score to others in your age group. By incorporating the age factor in the calculations, a percentile is obtained, which is much more accurate in risk assessment than the absolute number. The MESA CAC score calculator is an excellent tool for this purpose.

Interpreting Calcium Score Results

An optimal calcium score is usually 0. However, it’s crucial to remember that a score of 0 may not tell the whole story. When interpreting calcium score results, it’s essential to consider the following ranges:

CAC Score 0

A score of zero indicates no detectable calcified plaque in the coronary arteries. This is an optimal result and suggests a low risk of coronary artery disease. However, it does not rule out the presence of soft (non-calcified) plaques or the risk of future cardiac events, especially in younger individuals or those with other risk factors, such as diabetes, hypertension, smoking or hypercholesterolemia.

CAC Score 1-100

A score between 1 and 100 indicates mild calcification and a low to moderate risk of coronary artery disease. This range suggests the presence of some atherosclerotic plaque buildup, and the risk of a cardiac event is slightly higher than those with a score of zero. Lifestyle modifications and risk factor management are recommended.

CAC Score 101-300

101-300: A score between 101 and 300 indicates moderate calcification and a moderate to high risk of coronary artery disease. This range suggests a significant amount of atherosclerotic plaque buildup, and the risk of a cardiac event is higher than those with lower scores. Aggressive lifestyle modifications, risk factor management, and preventive medications may be necessary.

CAC Score above 300

A score of 300 or higher indicates extensive calcification and a high risk of coronary artery disease. This range suggests a substantial amount of atherosclerotic plaque buildup, and the risk of a cardiac event is significantly elevated. Intensive medical therapy, lifestyle modifications, and close monitoring are essential for individuals in this range.

A CAC score >300 is equivalent to prior ASCVD

A recent study by Budoff et al. (2023) found that patients with CAC scores >300 had an equivalent risk of major cardiovascular events as those with established cardiovascular disease (those with prior heart attack, coronary stent or bypass surgery). The study compared event rates in individuals without prior cardiac events across different CAC score categories to those with prior events. The results showed that individuals with CAC scores >300 had similar rates of heart attack and death to those with prior cardiac events. This finding suggests that patients with CAC scores >300 should be considered for intensive risk factor management and preventive therapies typically reserved for “secondary prevention” in patients with established coronary disease and prior heart attack.


Limitations of the Coronary Calcium Score Test

Calcium scoring is a valuable tool for assessing the risk of coronary artery disease (CAD). However, it is not an appropriate diagnostic approach for high-risk patients and those presenting with cardiac symptoms for several reasons:

Inability to detect soft, non-calcified plaque:

The CAC test measures the amount of calcified plaque within the coronary arteries but does not provide information about soft, non-calcified plaque. Soft plaques are more prone to rupture and can cause acute coronary events, such as heart attacks.

Non-calcified plaque with calcium score zero
Coronary Calcium Score test can miss large plaques with severe blockages, if there is no calcium deposit within them. (Soft Plaques)

Potential for false reassurance:

In high-risk patients or those with symptoms, a low or zero calcium score can be falsely reassuring, which leads to medication non-adherence and a false sense of well-being.

No functional assessment:

The CAC test detects calcified plaques but cannot provide any information as to whether these plaques have obstructed the coronary artery, i.e. “functional status”. It is possible for an individual to have a high calcium score but still have sufficient blood flow to the heart muscle (non-obstructive plaques) or vice versa. In such cases, additional diagnostic tests such as stress testing or coronary angiography may be necessary to evaluate the functional impact of the identified calcifications.

Real-life example: 

A 37-year-old man presents with shortness of breath and throat pain during exertion. Despite having significant traditional risk factors (hypertension, high cholesterol, prediabetes, and a sedentary lifestyle), a CT calcium score was ordered for him, which was 0. Unfortunately, this led to a false sense of reassurance, and he avoided medical therapy.

Due to persistent symptoms, further evaluation with a stress echocardiogram and CT coronary angiogram revealed a severe blockage in the left anterior descending (LAD) artery, which required a stent placement.

severe blockage before and after stenting
Severe proximal LAD stenosis. Before and after angioplasty
Video: Case study of severe coronary artery stenosis despite a calcium score of zero

This case highlights the importance of choosing the appropriate test for each patient and the potential consequences of relying solely on the calcium score in symptomatic or high-risk patients.

Here is the full video of the case with detailed explanation about the coronary plaques and calcifications. 

What is the difference between a CT calcium Score and a CT Coronary Angiogram (CTCA)?

While the calcium score is a risk assessment tool, CTCA is a diagnostic test that uses contrast dye to evaluate blood flow and identify narrowing or blockages in the coronary arteries.

CTCA is indicated for patients with symptoms suggestive of coronary artery disease, such as chest pain or breathlessness on exertion, abnormal stress echocardiogram results, or for pre-operative evaluation in certain cases. It provides detailed images of the coronary arteries but involves higher radiation exposure and the use of contrast dye.

In contrast, the calcium score quantifies calcified plaque burden without using contrast dye. It aids in risk stratification but lacks information about non-calcified plaque or blood flow impairment.

Difference between CT coronary angiogram CTCA and coronary calcium score CAC CT
Video: Case study of severe coronary artery stenosis despite a calcium score of zero

In this video I have explained the difference between CT Coronary Angiogram (CTCA) and CT Calcium Score in detail.

Frequently Asked Questions

How is the coronary calcium score test performed, and what is the cost?

  • The calcium score test is a non-invasive CT scan that does not require any special preparation. The cost varies depending on the location and healthcare provider. To learn more about the cost of a CAC score and how it is done, check this Coronary Calcium Score WebStory.

What is a normal calcium score?

  • A calcium score of 0 is optimal and normal, indicating no calcified plaque in the coronary arteries. However, it’s crucial to interpret the results in the context of other risk factors and age.

Can I reduce or reverse my calcium score?

  • No, you cannot reduce or reverse your calcium score. Once coronary artery calcification has occurred, it is generally irreversible. However, you can significantly lower your overall risk of cardiovascular events by addressing modifiable risk factors such as quitting smoking, adopting a healthy diet, engaging in regular physical activity, managing stress, controlling blood pressure and diabetes, and taking prescribed medications.
  • It is worth noting that your calcium score might increase after initiating statin therapy and incorporating exercise into your routine. This rise is not necessarily a negative development, as it could indicate that plaques are hardening and becoming more stable, reducing the risk of a heart attack. 

Is a calcium score test required for someone already on a statin?

  • The answer generally is no, but it depends on the case. If a patient is taking their medication regularly and their LDL-C levels are around 2 mmol/L (77 mg/dl), then there is no need for a CAC test. However, if the patient is taking statins infrequently and their LDL-C levels are significantly higher than 2 mmol/L, then a CAC test can be considered to help guide the therapy. Based on the results, a more relaxed or stricter approach to medical therapy can be taken. For example, if the score is 0 or very low, a more relaxed approach can be taken, and if the score is high, a stricter approach may be necessary.

Does a CT Coronary Angiogram (CTCA) show the calcium score?

  • Many radiology facilities automatically include calcium scores in CTCA reports, but some may only provide them if specifically requested. To ensure your report contains a calcium score, ask your doctor to order it alongside your CTCA.

If I can have a CT Coronary Angiogram (CTCA) that includes the calcium score, why should I only do a calcium score?

You raise a very valid point. While a CT Coronary Angiogram (CTCA) provides more detailed information, including the calcium score and visualization of non-calcified plaques, there are several reasons why we may choose to order a CAC score alone:

Radiation exposure:

Although CTCA is generally a safe procedure, it does expose the patient to a higher radiation dose than a CAC score. Minimizing radiation exposure is important for younger patients or those requiring repeated imaging.

Contrast use:

CTCA requires the injection of iodinated contrast, which can be problematic for patients with kidney dysfunction or allergies to contrast agents. 


CTCA is generally more expensive than a CAC score. The cost difference determines which test to order, especially for screening purposes in low to intermediate-risk patients.

Appropriate use:

The CAC score is only used for risk assessment in ASYMPTOMATIC individuals with a LOW-to-INTERMEDIATE risk of coronary artery disease. In these cases, a CAC score can provide valuable information to guide preventive measures and lifestyle modifications without requiring a more invasive and costly test like CTCA.

Avoiding overdiagnosis and overtreatment:

In the past 20 years, the evidence has been overwhelming that medical therapy is the best course of treatment for asymptomatic coronary artery disease or blockages. By finding “bystander” blockages, CTCA could lead to unnecessary anxiety, additional testing, or unnecessary invasive procedures, leading to complications. The preferred approach for treating ASYMPTOMATIC coronary disease is intensive medical therapy, and a healthy lifestyle and CAC score is just another tool in the box for the risk assessment.

However, it is essential to note that in SYMPTOMATIC patients or those with HIGH-RISK features, a CTCA may be the most appropriate test to evaluate the presence and extent of coronary artery disease. Ordering a CAC score vs CTCA should be based on a patient’s individual risk factors, symptoms, and the healthcare provider’s clinical judgment.

Should the calcium score test be repeated in the future?

    • Generally, if the calcium score is high, there is no need to repeat the test. A high score indicates an elevated risk, and the focus should be on intensive treatment of risk factors and lifestyle modifications. However, select patients with a calcium score of 0, especially younger individuals, could consider repeating the test in 5 years. This is particularly important if they have a few risk factors like high cholesterol or hypertension and decide against medical therapy.

Conclusion: The CAC score is only one piece of the puzzle

The CAC score is just one piece of the complex puzzle that makes up an individual’s risk for heart attack. As illustrated in the image, numerous factors contribute to this risk, including age, smoking, high cholesterol, obesity, diabetes, menopause, and inflammatory diseases. While an essential piece of the puzzle, the CAC score should never be interpreted in isolation without considering the whole picture.

Like any other medical test, the CAC score has pros and cons and should be used judiciously. It can help clarify someone’s risk for future heart disease, but CAC tets should not be used to investigate chest pain or ordered in high-risk patients. An important takeaway is that a high calcium score should never lead to an invasive coronary angiogram without considering the clinical context. This practice is harmful and not recommended.

In conclusion, the CAC score is a valuable tool in assessing cardiovascular risk, but it is essential to remember that it is just one component of a comprehensive risk assessment. When interpreting CAC score results, we should consider the full spectrum of risk factors and the individual patient’s clinical context before making further treatment decisions.

Coronary Artery Risk Factors

References and further reading

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