A coronary artery calcium score measures calcified plaque in the heart's arteries on a non-contrast CT scan, reported in Agatston units. A score of 0 means no calcium was seen and indicates a very low risk of events over five years. A score of 1 to 99 means some plaque, and 100 or more is a larger burden that pushes estimated risk higher.
The scan is a tool for sorting risk in people without symptoms. It is not a test for chest pain. This guide explains who it suits, how US, UK and Australian guidance differ, what a zero really means and how age percentiles work.
What does a coronary artery calcium score measure?
A coronary artery calcium (CAC) score measures how much calcified plaque sits in the coronary arteries, the vessels that supply the heart muscle. The 2023 Australian guideline for assessing and managing cardiovascular risk explains that the test uses computed tomography (CT) and, unlike coronary angiography, needs no contrast dye or intravenous line.
The result comes in two forms. The total score in Agatston units is an absolute measure of coronary calcium. The percentile compares that score with people of the same age, sex and ethnicity.
The Agatston method, described in a peer-reviewed primer on the CAC Data and Reporting System, counts lesions denser than 130 Hounsfield units, the CT scale for tissue density, with an area of at least 1 mm². Each lesion's area is multiplied by a density weighting and the totals are added.
Radiation exposure is low. The Australian guideline compares it with a mammogram, and the primer cites average effective doses, measured in millisieverts (mSv), of about 1.0 to 1.5 mSv for prospectively triggered scans and about 3.0 mSv for retrospectively gated scans. The Australian guideline also warns that the scan can find incidental problems, such as lung nodules, that lead to further tests.
What is a good calcium score? Reading 0, 1 to 99 and 100+
The best calcium score is 0. Above that, both the number and your age matter. The Society of Cardiovascular Computed Tomography reporting system, summarized in the primer, labels the risk of each band.
| Agatston score | Reporting system risk label | How US guidance uses it | How Australian guidance uses it |
|---|---|---|---|
| 0 | Very low | Can support deferring a statin in low or intermediate risk when no higher-risk condition applies (see below) | May move an intermediate-risk person to a lower category; consider retesting in 2 to 5 years |
| 1 to 99 | Mild | Any calcium supports an LDL cholesterol goal below 100 mg/dL | A score at or above the 75th percentile for age and sex may move risk up |
| 100 or more | Moderate (100 to 299), moderate to severe (300 or more) | Lower LDL cholesterol targets as calcium rises | Above 99 may move low or intermediate risk to a higher category |
The US column comes from the ACC and AHA announcement of the 2026 dyslipidemia guideline and an ACC summary of how the guideline changes practice. The Australian column comes from the 2023 guideline.
Who should get a CAC scan?
A CAC scan suits adults without symptoms whose need for cholesterol-lowering treatment is uncertain. It is not a screening test for everyone.
United States. The 2026 guideline recommends a CAC scan for men aged 40 and older and women aged 45 and older with a borderline or intermediate 10-year risk, if knowing the score will help decide whether to prescribe a statin. Using the PREVENT risk equations, borderline means 3% to less than 5% and intermediate means 5% to less than 10%.
United Kingdom. NICE guideline NG238 bases risk assessment on the QRISK3 tool for adults aged 25 to 84 without cardiovascular disease, and its recommendations do not include coronary calcium scoring. If you are considering a scan, ask your GP how a result would fit into a QRISK3-based plan.
Australia. The 2023 guideline makes a strong recommendation against CAC scoring for general population screening. It advises against measuring CAC in people with known coronary heart disease or who are already at high risk, because treatment is indicated regardless. Reclassifying risk with a CAC score can be considered when treatment decisions are uncertain, for example when risk is low or intermediate but other concerns are present. The guideline notes that CAC testing is not presently subsidized by Medicare and that cost varies considerably between providers.
Does a zero calcium score mean no risk?
A zero calcium score means very low risk, not no risk. The Australian guideline states that a score of 0 indicates a very low risk of cardiovascular events and death within five years, but does not rule out non-calcified atherosclerosis, particularly in younger people. Its value is highly dependent on age.
The primer adds that CAC scoring cannot detect non-calcified plaque, so a negative scan cannot rule out a significant blockage in someone with symptoms.
Zero can also change over time. The Australian guideline cites a prospective cohort in which 25% of people with a zero score developed coronary calcium within five years, and considers retesting within 2 to 5 years reasonable.
CAC score by age: what the percentile means
A CAC percentile shows how your score compares with people of the same age, sex and ethnicity.
The US Multi-Ethnic Study of Atherosclerosis offers a MESA calcium calculator covering ages 45 to 84, men and women, and four groups: Black, Chinese, Hispanic and White. You can optionally enter an observed Agatston score to see where it sits.
The Australian guideline cautions that percentiles may be based on different populations depending on the software, so clarify the report with the imaging provider. It also notes that CAC rises with age and may discriminate less well after 75, when most people have high scores.
Calcium score and statins
A calcium score mainly informs whether to start or intensify cholesterol-lowering treatment. Under the 2026 US guideline, any amount of coronary calcium supports an LDL cholesterol goal below 100 mg/dL, with lower targets at higher amounts. A score of zero can support deferring a statin in a low or intermediate-risk adult, after discussion with a clinician. It does not override a statin indication that stands on its own, such as familial hypercholesterolemia, an LDL cholesterol of 190 mg/dL or more, or diabetes in midlife. The 2018 AHA/ACC cholesterol guideline also named diabetes, a family history of premature heart disease and cigarette smoking as conditions where a zero score should not be taken as reassurance.
The Australian guideline adds that a high score above 99, shown and explained to the person, may support shared decision-making and help with treatment hesitancy. It also says not to repeat a scan if the result would not change management, for example in someone already taking long-term blood pressure or lipid-lowering treatment.
Read the score alongside your cholesterol panel and the rest of your risk assessment, not on its own.
Practical checks before and after a calcium scan
1. Name the decision the score will change.
Before booking, write down what you and your clinician would do differently with a score of 0 versus 150. If nothing would change, the scan is unlikely to help.
2. Confirm you are the right candidate.
Check that you have no symptoms, no known coronary heart disease and are not already classed as high risk. Those situations call for treatment or a different test.
3. Read the score and the percentile together.
Note the total Agatston score, the percentile and the reference population used. Ask the imaging provider if the report does not say.
4. Ask about incidental findings.
Find out how lung nodules or other findings will be reported and who arranges follow-up.
5. Keep the report and the date.
A repeat scan only makes sense if it could change management, and the interval depends on the first result.
Chest pain is an emergency, not a scan question
A coronary calcium score should never be used to decide whether chest pain is serious. The Australian guideline states that it should not be used as a standalone test for people with symptoms such as possible angina.
The NHS heart attack guidance says to call 999 for chest pain that feels tight or squeezing, chest pain spreading to the arms, neck or jaw, severe difficulty breathing, or pale, blue or gray lips or skin. Call 911 in the US, 999 in the UK or 000 in Australia, as explained in healthdirect's triple zero guidance. Do not drive yourself.
For non-urgent risk factors, accurate home blood pressure readings feed into the same risk estimate the scan is meant to refine.
Frequently asked questions
What is a good calcium score?
A score of 0 is the best result and indicates a very low risk of cardiovascular events over five years. Scores of 1 to 99 show mild calcified plaque, and 100 or more indicates a larger burden. Because calcium rises with age, ask for the percentile for your age, sex and ethnicity alongside the total score.
Who should get a CAC scan?
A CAC scan suits adults without symptoms whose need for a statin is uncertain. The 2026 US guideline recommends it for men from 40 and women from 45 at borderline or intermediate risk. Australian guidance advises against population screening, and NICE's UK risk guideline does not include calcium scoring in its recommendations.
Does a calcium score of zero mean no risk?
No. Australian guidance says a zero score indicates very low risk over five years but does not rule out non-calcified plaque, especially in younger people. The scan cannot detect soft plaque or rule out a blockage in someone with symptoms, and a quarter of people with zero developed calcium within five years in one cohort.
Does a coronary calcium scan use radiation or contrast?
A calcium scan uses low-dose CT without contrast dye or an intravenous line. Australian guidance compares the radiation to a mammogram, and a peer-reviewed primer cites average doses of about 1.0 to 1.5 mSv for prospectively triggered scans. The scan can also reveal incidental findings, such as lung nodules, that need follow-up.
Should calcium scores be repeated?
Only if a new result could change management. Australian guidance suggests considering a repeat in 2 to 5 years after a zero score, depending on baseline risk. It advises against repeating the scan for people whose treatment would not change, such as those already on long-term blood pressure or lipid-lowering treatment.
The short version
A coronary artery calcium score measures calcified plaque on a low-dose, non-contrast CT scan. Zero means very low short-term risk but not zero risk, 1 to 99 means some plaque, and 100 or more pushes risk and treatment goals higher. US guidance recommends selective scanning for borderline or intermediate risk, Australia advises against population screening and does not subsidize it through Medicare, and NICE does not include it. Chest pain needs an emergency call, not a scan.
This article is general education, not medical advice. It does not replace your own physician.
