A plain-English guide
What is a coronary calcium score, and how does the scoring work?
A coronary artery calcium score is a number from a simple CT scan of your heart. It estimates how much hard, calcified plaque has built up in the arteries that supply your heart muscle. Below, we explain what the scan shows, how the score is worked out, what each range means, and the research behind it.
- 10-15 min
- Time on the scanner
- No dye
- No needles or contrast
- Low dose
- Typically around 1 mSv
The basics
Why calcium is a useful warning sign
Atherosclerosis begins when fatty deposits build up inside the artery wall. As these deposits age and the body tries to repair them, calcium gets laid down inside them. Calcium in a coronary artery is not normal: it is a sign of established plaque.
Because calcium is very dense, it shows up clearly on CT without any dye. This makes it easy to measure reliably. The total amount of calcium generally tracks with the total amount of plaque in the arteries, which in turn tracks with the chance of a future heart attack.
The important caveat: early, soft plaque contains little or no calcium. So a score of zero means low risk, not no risk. It also does not measure how narrow an artery is, so it cannot diagnose or rule out a blockage that is causing symptoms.
Step by step
What happens during the scan
- 01
Preparation
No fasting, no needles and no dye. You may be asked to avoid caffeine before the scan. Small stickers are placed on your chest so the scanner can time the pictures with your heartbeat.
- 02
Scan
You lie on the scanner bed and hold your breath for a few seconds while a low-dose CT scan takes thin pictures of your heart. You are usually on the table for 10-15 minutes.
- 03
Scoring
A computer program finds every area of calcium in the heart arteries, measures its size, assigns a density weight, and adds everything together to produce your total Agatston score.
- 04
Review
A radiologist reports the total score and its distribution. A doctor then reads it alongside your age, sex, blood pressure, cholesterol, blood sugar, smoking history and family history.
How the score is calculated
Size multiplied by density
The scoring system is like a weighted count of all calcified spots. Each spot is measured in square millimetres, then multiplied by a density factor based on its brightness on the scan (measured in Hounsfield units, or HU):
x1
130 - 199 HU
x2
200 - 299 HU
x3
300 - 399 HU
x4
400 HU and above
The weighted scores are added together across all four major coronary arteries. For example, a single 8 mm² spot that peaks at 420 HU contributes 8 x 4 = 32 to the total. The final sum is your Agatston score.
The score ranges
What the numbers mean in practice
These bands are the standard categories used in reports and in large studies. They describe plaque burden, not a diagnosis, and they should always be read alongside your age, sex and other risk factors.
| Agatston score | Plaque burden | What it generally indicates |
|---|---|---|
| 0 | No calcified plaque | The scan did not find any calcium in your coronary arteries. This is the best possible result and means your risk of a heart attack over the next decade is very low. A zero score does not rule out all artery disease, though, so other risk factors such as smoking, diabetes and family history still matter. |
| 1 - 10 | Minimal | A tiny amount of calcified plaque is present. This is early coronary artery disease. It is usually managed with lifestyle changes, such as diet, exercise and stopping smoking, plus keeping blood pressure, cholesterol and blood sugar in a healthy range. |
| 11 - 100 | Mild | A mild build-up of plaque is present. This is a sign of mild coronary artery disease and usually prompts a closer look at risk factors, especially cholesterol and blood pressure. |
| 101 - 400 | Moderate | A moderate amount of plaque is present. Your risk of a future heart problem is higher than average for your age. Guidelines generally recommend more intensive preventive treatment, such as stricter cholesterol and blood pressure targets. |
| over 400 | Extensive | A large amount of calcified plaque is present, indicating a high risk of a heart attack or other cardiac event. This usually warrants intensive treatment and a discussion with a cardiologist, especially if you have any symptoms. |
Percentiles: how you compare to people your age
Calcium tends to build up as people get older, so the same score can mean different things at 45 and at 75. Reports often include a percentile that compares your score to other people of the same age, sex and ethnicity. A score of 80 might be above the 90th percentile for a 45-year-old woman but around average for a 70-year-old man. A high percentile with a modest score suggests plaque is forming earlier than expected.
How doctors use the result
Coronary calcium scoring is mainly used to help people whose calculated risk is in a grey zone. A zero score can support delaying or avoiding preventive medication in some people, while a score above 100, or above the 75th percentile for your age and sex, usually strengthens the case for more intensive prevention. The final decision is made by you and your doctor.
Not for everyone
Who a calcium score is not useful for
A calcium score is a powerful tool for the right person, but it is not the right test for everyone. If any of the following apply to you, a different assessment may be more useful.
You already have known heart disease
If you have already had a heart attack, angina, stent, bypass surgery or a known coronary artery blockage, your treatment plan is already based on that diagnosis. A calcium score is unlikely to change what you and your doctor do next.
You have symptoms that need urgent checking
Chest pain, pressure, shortness of breath, unexplained fainting or palpitations should be assessed urgently with a clinician. A calcium score is not a rule-out test for these symptoms.
You are under 40 with no strong risk factors
Calcium is uncommon in younger adults, and a zero score is expected. If you are otherwise low risk, the result rarely changes management and you may be better off focusing on lifestyle and standard risk assessment.
You are over 75 with very high baseline risk
By this age, calcium is common and many people already qualify for preventive treatment based on age and other risk factors alone. The result is less likely to reclassify your risk enough to change your plan.
You are pregnant or breastfeeding
Any CT scan involves radiation, so it is generally avoided during pregnancy unless there is a clear, urgent medical reason. If you are breastfeeding, discuss timing with your doctor.
You cannot lie flat or hold your breath briefly
The scan requires you to lie still on a narrow table and hold your breath for a few seconds. Severe claustrophobia, mobility problems, certain arrhythmias or an inability to follow breathing instructions can make the images unusable.
Bottom line: If you are unsure whether a calcium score is right for you, speak with your doctor first. HeartScore includes a doctor consult in every visit so the result can be interpreted safely and personally.
What it cannot do
Important limits of a calcium score
It is not a test for chest pain
If you have chest pain, breathlessness or other symptoms, you need a clinical assessment and possibly different tests. Calcium scoring is for people without symptoms who want to refine their risk.
It does not measure narrowing
A high score tells you plaque is present, but not whether an artery is significantly narrowed. That requires a CT coronary angiogram or a functional test such as a stress test.
Zero is low risk, not no risk
Soft, non-calcified plaque is invisible on this scan. Smoking, diabetes, a strong family history and very high cholesterol still need attention even if the score is zero.
Scores usually rise over time
Calcium generally increases with age, even when treatment is working well, because plaque can stabilise as it calcifies. Repeat scans are not usually used to track treatment success.
There is a small radiation dose
A modern calcium scan is typically around 1 mSv, similar to a few months of natural background radiation in Australia. It is low, but not zero, so the scan should have a clear reason.
It needs clinical context
The number only becomes useful once it is combined with your blood pressure, cholesterol, blood sugar, smoking status and family history. That is why a doctor consult is included.
Evidence
Key studies and guidelines
Links to the main research and guidance so you can read the source material for yourself.
MESA: coronary calcium predicts heart events across ethnic groups
Detrano et al., New England Journal of Medicine, 2008. In 6,722 adults without known heart disease, doubling of the calcium score increased the risk of a major coronary event by 15-35%.
Agatston: the original scoring method
Agatston et al., Journal of the American College of Cardiology, 1990. This is the paper that defined the Agatston score still used today.
MESA coronary calcium percentile calculator
A free tool from the MESA study that compares your score to people of the same age, sex and ethnicity.
2018 AHA/ACC cholesterol guideline
Recommends coronary calcium scoring to help decide whether someone should start a statin, including using a score of 0 to defer treatment in selected people.
A score of 0 as a negative risk marker
Blaha et al., systematic review showing that a zero calcium score identifies a low-risk group over 10-15 years of follow-up.
Australian guidance: cardiovascular disease risk assessment
The Australian guideline on assessing and managing cardiovascular disease risk, including the role of coronary calcium scoring as a risk-reclassification tool.
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