Calcium Scoring CT / CAC Scan
What is a Calcium Scoring CT?
A Calcium Scoring CT, also known as a Coronary Artery Calcium (CAC) scan, is a specialised CT scan that looks for calcium deposits in the walls of the coronary arteries. These blood vessels supply oxygen-rich blood to the heart muscle.
Calcium in a coronary artery is a marker of coronary atherosclerosis, the process in which plaque builds up within artery walls. The presence and amount of coronary artery calcium can therefore provide useful information about a person's risk of developing coronary artery disease and having a heart attack in the future.
A CAC scan is quick, non-invasive and usually does not require an injection or contrast dye.
The scan produces a coronary calcium score, often called an Agatston score. In general, a higher score indicates greater calcified coronary plaque and a higher risk of future cardiovascular events.
Who is Suitable for a Calcium Scoring CT?
A CAC scan may be considered when a doctor wants more information about a person's cardiovascular risk before deciding whether preventive treatment is appropriate.
It may be particularly useful for people who are considered to have an intermediate or uncertain risk of cardiovascular disease based on factors such as:
- increasing age
- high cholesterol
- high blood pressure
- smoking or a previous history of smoking
- diabetes or other metabolic risk factors
- being overweight or obese
- a sedentary lifestyle
- a family history of premature coronary artery disease
- uncertainty about whether cholesterol-lowering medication should be commenced.
Calcium scoring can provide additional information beyond traditional cardiovascular risk factors.
For example, a person may have moderately elevated cholesterol but no other major risk factors. A CAC scan may help their doctor better assess their overall risk and discuss whether preventive treatment is appropriate.
CAC scanning is not necessary for everyone. Your doctor will consider your age, medical history, cardiovascular risk factors and previous investigations before recommending the test.
Benefits of a Calcium Scoring CT
One of the main benefits of calcium scoring is its ability to detect evidence of coronary atherosclerosis before symptoms develop.
Potential benefits include:
- identifying calcified plaque in the coronary arteries
- providing additional information about future cardiovascular risk
- helping refine a person's cardiovascular risk assessment
- identifying people who may benefit from more intensive prevention
- helping guide discussions about cholesterol-lowering medication and other preventive measures
- providing additional motivation to address modifiable risk factors.
The scan itself is also relatively simple. It is usually completed within a few minutes and does not normally require needles, contrast dye or hospital admission.
What Does a Coronary Calcium Score Mean?
The CT images are analysed to calculate a numerical calcium score. The most commonly used measurement is the Agatston score.
As a general guide:
- CAC score of 0: no detectable coronary artery calcium
- CAC score of 1–99: a small amount of calcified plaque
- CAC score of 100–399: a moderate amount of calcified plaque
- CAC score of 400 or more: a substantial amount of calcified plaque.
These numbers should not be considered in isolation.
Age, sex, overall cardiovascular risk, symptoms, cholesterol levels, blood pressure, diabetes, smoking history and family history can all influence the significance of a CAC result.
A score of zero is generally reassuring and is associated with a relatively low risk of a cardiovascular event over the following years. However, it does not guarantee that the coronary arteries are completely free of disease. Calcium scoring may not detect early or non-calcified plaque.
Conversely, a high calcium score does not necessarily mean that a coronary artery is severely narrowed. It indicates a greater overall burden of calcified coronary atherosclerosis and a higher cardiovascular risk.
What to do Before a Calcium Scoring CT?
You usually need very little preparation for a CAC scan.
You will be asked to:
- avoid caffeine, smoking & strenuous exercise for 12hours before the scan
- continue your usual medications unless advised otherwise
- remove jewellery or other metal objects from the chest area
- wear clothing without metal fasteners. Disposable gowns are available.
It is important to tell the imaging practice if you are pregnant or think you may be pregnant because CT scanning uses X-rays.
Unlike a CT coronary angiogram, a standard calcium scoring CT generally does not require intravenous contrast.
Does Medicare cover a Calcium Scoring CT?
Medicare generally does not cover a Calcium Scoring CT. This means patients will usually need to pay the cost of the scan themselves.
Costs vary between radiology providers, so you may want to ask the imaging practice about the fee when making your appointment.
Although there is usually an out-of-pocket cost, a Calcium Scoring CT can provide useful additional information about your risk of coronary artery disease. Your doctor or cardiologist can advise whether the test is appropriate for you and whether the result is likely to influence your cardiovascular prevention or treatment plan.
What Happens During a Calcium Scoring CT?
The test is performed using a CT scanner.
Small adhesive electrodes are placed on the chest and connected to an electrocardiogram (ECG). This lets the CT scanner synchronise image acquisition with your heartbeat, reducing motion and producing clearer images of the coronary arteries.
You will lie on a table that moves through the CT scanner.
During image acquisition, you will usually be asked to hold your breath for a short period. The scanner then takes detailed images of the heart and coronary arteries.
The actual scan is very quick, taking only seconds, although the entire appointment usually takes longer to allow for preparation and positioning.
The procedure is painless.
What to Expect After a Calcium Scoring CT?
Generally, there is no recovery period after a calcium scoring CT.
Because contrast dye and sedation are not usually required, most people can leave immediately after the scan and return to their normal activities.
A radiologist or other appropriately trained specialist will analyse the images and calculate the coronary calcium score. The report is then provided to your referring doctor.
Your doctor will interpret the result alongside your other cardiovascular risk factors.
What Happens if My Calcium Score is High?
A high calcium score indicates that coronary atherosclerosis is present and that the overall burden of calcified plaque is greater.
It does not automatically mean that surgery, a stent or another cardiac procedure is required.
Instead, your doctor may use the result to consider whether cardiovascular risk factors should be managed more intensively. Depending on your individual circumstances, this may include:
- cholesterol-lowering treatment such as a statin
- management of high blood pressure
- improved diabetes management
- stopping smoking
- regular physical activity
- maintaining a healthy weight
- improving diet
- addressing other cardiovascular risk factors.
In some people, particularly those with symptoms or other concerning findings, clinicians may recommend additional cardiac investigations.
What are the Limitations of Calcium Scoring?
Calcium scoring is a valuable cardiovascular risk-assessment tool, but it has limitations.
The test detects calcified coronary plaque. It does not reliably identify non-calcified or "soft" plaque, which can also be associated with coronary artery disease.
A calcium scoring CT also does not directly show how much an artery has narrowed. A person can have a high calcium score without a critical narrowing, while another person may have significant non-calcified plaque despite having a low calcium score.
For these reasons, a CAC scan should not replace medical assessment or other investigations when symptoms suggest possible coronary artery disease.
Is a Calcium Scoring CT the Same as a CT Coronary Angiogram?
No. Although both use CT technology to examine the coronary arteries, they provide different information.
A calcium scoring CT measures the amount of calcified plaque in the coronary arteries. It generally does not require contrast dye and is primarily used for cardiovascular risk assessment.
A CT coronary angiogram (CTCA) uses intravenous contrast dye to provide detailed images of the coronary arteries. It can detect both calcified and non-calcified plaque and help determine whether an artery has narrowed.
Your doctor will recommend the investigation that is most appropriate for your circumstances.
Calcium Scoring CT Risks
Calcium scoring is considered a low-risk investigation.
The main consideration is exposure to a small amount of ionising radiation. Modern CT scanners and calcium-scoring protocols are designed to minimise radiation exposure while obtaining diagnostic-quality images.
Because radiation is involved, perform the test only when there is a reasonable clinical indication, rather than as a routine screening test for everyone.
Incidental findings are also possible. Because the CT scan includes structures around the heart, it may occasionally detect abnormalities unrelated to the coronary arteries that require further assessment.
When Should Calcium Scoring Not Be Used?
Calcium scoring is generally not the appropriate first investigation for someone experiencing symptoms that could indicate coronary artery disease, particularly new or worsening chest pain.
Symptoms such as:
- chest pressure, tightness or pain
- unexplained shortness of breath
- chest discomfort during physical activity
- pain spreading to the arm, shoulder, neck, jaw or back
- unexplained sweating, nausea or dizziness
require appropriate medical assessment.
Depending on the circumstances, other investigations, such as an ECG, blood tests, stress testing, or CT coronary angiography, may be more appropriate.
New, severe or persistent chest pain, particularly when associated with breathlessness, sweating, nausea or pain spreading to the arm or jaw, should be treated as a medical emergency.
