Coronary Artery Calcium Score: What Does It Actually Mean?

What is coronary artery calcium?

Atherosclerosis is the process in which plaque develops within arteries.

Over time, some coronary plaque becomes calcified.

Calcium within the walls of the coronary arteries can be detected very clearly using CT.

A CAC scan therefore provides a direct measure of calcified coronary atherosclerotic plaque burden.

The most commonly used measurement is the Agatston score.

How is the scan performed?

CAC scoring usually uses:

• —an ECG-gated CT scan
• —no intravenous contrast
• —a relatively short acquisition
• —a comparatively low radiation dose.

Small electrodes are placed on your chest so the scanner can synchronise the images with your heartbeat.

The actual CT acquisition is usually very quick.

What does a calcium score of zero mean?

A score of 0 means that no calcified coronary plaque was detected on the scan.

This is generally associated with a lower risk of future coronary events than when coronary calcium is present.^[3,4]

Large cohort studies such as the Multi-Ethnic Study of Atherosclerosis (MESA) have demonstrated the strong favourable prognostic value of a CAC score of zero.^[4]

However:

Risk is also influenced by factors such as:

• —smoking
• —diabetes
• —high blood pressure
• —cholesterol
• —family history
• —age
• —kidney disease
• —other medical conditions.

A score of zero should therefore be interpreted in context rather than used as permission to ignore cardiovascular risk factors.

What does a score between 1 and 99 mean?

Any CAC score above zero means that calcified coronary atherosclerosis is present.

A score between 1 and 99 generally represents a relatively smaller burden of calcified plaque than higher scores.

How important that is depends heavily on the individual.

For example, the same score may carry different implications in a younger person compared with someone much older.

What does a score of 100 or more mean?

As CAC burden increases, future cardiovascular risk generally increases.

Scores of 100 or more identify a more substantial amount of calcified coronary plaque and may meaningfully alter risk discussions in appropriately selected patients.^[3]

Scores are often broadly grouped as:

• —0
• —1–99
• —100–399
• —400 or more.

These are useful categories, but they are not treatment instructions by themselves.

What does a calcium score above 400 mean?

A CAC score of 400 or more represents a high burden of calcified coronary atherosclerosis.

It should prompt careful assessment of the person's overall cardiovascular risk and appropriate discussion with their healthcare professional.

Importantly, a high score does not tell us exactly how narrowed an individual coronary artery is.

CAC scoring measures plaque burden, not the severity of a particular coronary stenosis.

Is a calcium score the same as a CT coronary angiogram?

No.

They are different examinations.

Coronary calcium score

• —normally performed without intravenous contrast
• —measures calcified coronary plaque
• —gives an Agatston calcium score
• —primarily used for cardiovascular risk assessment in selected people.

CT coronary angiography

• —usually requires intravenous contrast
• —directly images the lumen and walls of the coronary arteries
• —assesses both calcified and non-calcified plaque
• —can identify coronary narrowing.

Should everyone have a calcium score?

No.

In the UK, cardiovascular prevention generally begins with assessment of established risk factors.

NICE recommends QRISK3 to estimate 10-year cardiovascular risk for many adults aged 25–84 without established cardiovascular disease.^[1]

CAC scoring can provide additional risk information in selected circumstances, and international cardiovascular guidelines use it particularly when treatment decisions remain uncertain after conventional risk assessment.^[3]

However, it is not a universal screening test for everyone.

Whether it is useful depends on:

• —age
• —baseline cardiovascular risk
• —symptoms
• —family history
• —existing disease
• —whether the result is actually likely to change management.

What is QRISK3?

QRISK3 is a UK cardiovascular-risk calculator.

It estimates the chance of developing cardiovascular disease over the following 10 years using factors such as:

• —age
• —sex
• —smoking
• —blood pressure
• —cholesterol
• —diabetes
• —ethnicity
• —kidney disease
• —several other medical conditions and treatments.

NICE currently recommends QRISK3 for formal cardiovascular risk assessment in many people aged 25–84 years who do not already have cardiovascular disease.^[1]

Risk scores are useful decision aids, but they are estimates rather than predictions of exactly what will happen to one individual.

External validation work confirms that QRISK3 can stratify risk, while also demonstrating the limitations inherent in any population-based prediction model.^[2]

If I have coronary calcium, what can I do?

The most important response is not to panic.

Coronary calcium is evidence of atherosclerosis, but cardiovascular risk is modifiable.

Depending on your overall risk profile, discussion with your GP or specialist may include:

• —cholesterol and lipid-lowering treatment
• —blood-pressure control
• —stopping smoking
• —diabetes management
• —regular physical activity
• —diet
• —maintaining a healthy weight
• —sleep
• —other individual cardiovascular risk factors.

Do not start, stop or change prescription medication solely because of an online article or calcium-score number.

Discuss the result with a healthcare professional who can interpret it alongside your complete risk profile.

Does taking a statin remove coronary calcium?

CAC scoring is primarily used as a risk marker, not as a test for monitoring whether treatment is “working”.

Changes in plaque biology during treatment are more complicated than simply expecting the calcium score to fall.

For that reason, serial calcium scoring should not be treated like repeatedly checking cholesterol or blood pressure.

Should I repeat my calcium score?

There is no single repeat interval suitable for everybody.

Among people with CAC 0 in MESA, development of detectable coronary calcium varied according to individual characteristics. One analysis estimated that a potential rescan interval might fall broadly within approximately 3–7 years depending on the person's risk profile.^[4]

That does not mean everyone with CAC 0 should automatically be rescanned.

The decision should depend on whether repeating the test is likely to alter management.

Questions to discuss with your doctor

If you have had a CAC score, useful questions include:

• —What is my overall cardiovascular risk?
• —What is my QRISK3 score?
• —Does this calcium result change what you recommend?
• —Should my cholesterol treatment change?
• —Is my blood pressure adequately controlled?
• —Do my smoking, diabetes or family-history risks change the interpretation?
• —Do I actually need any further cardiac imaging?