Coronary calcium score: what your CAC number means, by band and by age

Plaque in a heart artery starts soft and slowly hardens as calcium settles into it. A calcium scan photographs that hardened part. The result is a single number that tells you, and your clinician, how much coronary artery disease has already built up, which is often more useful for a treatment decision than an estimate from age and cholesterol alone.

How the scan works

A calcium scan is a low-dose CT of the chest, timed to your heartbeat with ECG stickers so the image is taken while the heart is still. You lie on the table and hold your breath for a few seconds at a time; the scanning itself takes well under a minute, and RadiologyInfo, the patient site of the American College of Radiology and the Radiological Society of North America, says the whole exam takes less than 20 minutes ¹. There is no contrast dye. The dose is low, generally about 1 to 2 mSv; for comparison, a person in the US receives roughly 3 mSv a year from natural background radiation.

How the Agatston number is calculated

In short, the software adds up every speck of calcium in the heart arteries and gives brighter, denser specks more weight. The standard method is the Agatston score, named after the cardiologist Arthur Agatston, whose team described it in 1990 ². The software flags every spot with a density of at least 130 Hounsfield units (HU, the scale CT uses for density: water is 0, bone is several hundred). For each spot it multiplies the area in square millimetres by a weight set by the brightest point in that spot, then adds every spot in every artery together.

So a total Agatston score of 100 can come from one dense patch or several faint ones. Some reports add a volume score (the calcium volume in cubic millimetres, with no weighting). In MESA, the Multi-Ethnic Study of Atherosclerosis, a long-running US study funded by the National Heart, Lung, and Blood Institute, Michael Criqui and colleagues found that at any given calcium volume, denser calcium was linked to lower coronary risk ³. Dense calcium tends to sit in older, more settled plaque.

What the scan cannot see

The calcium score is a record of plaque that has already hardened. Young, soft plaque does not show up, and neither does how narrow the inside of the artery has become. Because of this, a zero is reassuring without being a guarantee, the score can rise on a statin, and the scan belongs beside blood tests that measure the drivers of plaque.

What your score means: 0, 1 to 99, 100 to 299, 300 and above, 1,000 and above

Event risk rises steadily with the score. In MESA, which followed 6,722 adults without known heart disease, people scoring 101 to 300 had about 7.7 times the risk of a coronary event of people scoring 0, after allowing for age, cholesterol and other risk factors, and people above 300 had about 9.7 times the risk ⁴. The score predicted events in white, Black, Hispanic and Chinese American participants alike.

The bands below follow the CAC-DRS reporting standard of the Society of Cardiovascular Computed Tomography ⁵ and the 2018 US cholesterol guideline ⁶. The 1,000-plus group comes from the CAC Consortium, a study of 66,636 adults without symptoms: people scoring 1,000 or more had about 5 times the risk of dying from heart disease of people scoring 0, and clearly higher risk than people scoring 400 to 999 ⁷.

Patients with extensive CAC (CAC ≥1,000) represent a unique very high-risk phenotype with mortality outcomes commensurate with high-risk secondary prevention patients.Peng AW et al., CAC Consortium, JACC: Cardiovascular Imaging 2020 ⁷

You will see more than one band system. CAC-DRS uses 0, 1 to 99, 100 to 299 and 300 or more, and adds a vessel count ⁵. Many reports and websites still use 1 to 99, 100 to 399 and 400 or more, and some use finer older bands: RadiologyInfo lists 1 to 10 as minimal, 11 to 100 as mild, 101 to 400 as moderate and over 400 as extensive ¹. The number is the same; only the labels differ.

Reading your report line by line

A typical report carries five things. The total Agatston score is the headline. Per-artery scores split that total across the left main (LM), left anterior descending (LAD), left circumflex (LCx) and right coronary artery (RCA). A vessel count, written V1 to V4 under CAC-DRS, says how many of those four arteries have any calcium ⁵. A percentile compares your total with people of the same age, sex and usually ethnicity. Last comes a note on anything else seen in the scanned area, such as a lung nodule.

Two details carry more weight than the total suggests. Calcium in the left main artery matters because that artery feeds most of the left side of the heart. Calcium spread across three or four vessels predicts higher risk than the same total confined to one ⁵.

What is a normal calcium score for my age?

Calcium builds with age, is higher in men than women at the same age, and differs by ethnicity. The MESA reference tables come from 6,110 adults free of heart disease and treated diabetes, and they are why your report gives an age-, sex- and ethnicity-matched percentile ⁸. In those tables, calcium amount and prevalence rise steadily with each age band, men run higher than women, and among men white participants have the highest percentiles. For most women under about 65, and for many men in their 40s, the middle (median) score is 0.

A score of zero: how reassuring is it?

A zero is the most reassuring result a person without symptoms can get from this scan, and it is still a snapshot. Soft plaque can be present with no calcium yet. In the CONFIRM registry, an international study of more than 10,000 people with symptoms who had both a calcium score and a CT angiogram (a CT scan with dye that shows narrowing), 3.5% of those with a score of 0 still had an artery narrowed by 50% or more ⁹. That is why a zero never clears chest pain.

A zero also has a shelf life. In 3,116 MESA participants who started at 0, Omar Dzaye and colleagues estimated the warranty period of a zero score, the time before a repeat scan has a reasonable chance of turning positive, at 3 to 7 years depending on sex and ethnicity; <a href="/conditions/diabetes">diabetes</a> shortened it most ¹⁰. The 2018 guideline says that with a score of zero it is reasonable to hold off a statin and reassess in 5 to 10 years, unless diabetes, a family history of premature heart disease, or smoking is present ⁶.

Who a calcium scan is for, and who it is not for

The 2018 US guideline places the scan with adults aged 40 to 75 at borderline or intermediate 10-year risk (5% to under 20%) when the decision about starting a statin is uncertain ⁶. Your 10-year risk is an estimate your clinician works out from your age, sex, blood pressure, cholesterol, diabetes and smoking status, using a tool such as the PREVENT or Pooled Cohort Equations calculator; ask for this number before booking a scan. Outside the US the support is softer. The 2021 European Society of Cardiology prevention guideline says a calcium score may be considered to refine risk near treatment thresholds, its weakest level of recommendation ¹¹, and the US Preventive Services Task Force judged the evidence insufficient to recommend adding the score to routine risk assessment in adults without symptoms ¹².

• A good fit: adults 40 to 75 without symptoms, at borderline or intermediate risk, unsure whether a statin is worth it.
• A good fit: people whose family history worries them but whose standard risk estimate comes out low or middling.
• Usually not useful: people already on a statin for high LDL, diabetes or known heart disease, where the scan will not change treatment.
• Not the right test: anyone with chest pain or other heart symptoms, who needs a diagnostic test instead.
• Not advised: pregnancy, and young adults at very low risk, where a zero is expected and the radiation buys little.

Calcium score plus your blood tests

The scan and a blood panel answer different questions. The calcium score shows how much plaque has built up and hardened so far. <a href="/biomarkers/apolipoprotein-b">ApoB</a>, LDL cholesterol and Lp(a) measure the particles that drive new plaque, <a href="/compare/hs-crp-vs-crp">hs-CRP</a> reflects low-grade inflammation, and <a href="/biomarkers/hba1c">HbA1c</a> reflects blood sugar. A zero score with a high ApoB means little damage yet from a driver that is still running; a high score with a normal ApoB often means damage from years before the numbers came down. On which lipid number tracks that driver best, our <a href="/compare/apob-vs-ldl">ApoB vs LDL comparison</a> sets out why ApoB counts the particles while LDL measures the cholesterol they carry. For a walk-through of every heart blood test, see <a href="/learn/cardiac-markers-explained">cardiac markers explained</a>.

Lp(a) is the clearest case for reading both together. In 6,590 adults from MESA and the Dallas Heart Study, Anurag Mehta and colleagues found that a high <a href="/biomarkers/lipoprotein-a/high">Lp(a)</a> and a score of 100 or more each raised risk on their own, and people with both had the highest risk, about 4.7 times that of people with neither ¹³. In the same study, a high Lp(a) with a score of 0 did not carry a clearly higher risk over 13 years.

CalculatorLDL calculatorIf your lipid panel gives total cholesterol, HDL and triglycerides, this works out LDL with the newer equation.Work it out

New to lipid panels? Start with <a href="/learn/how-to-read-your-lipid-panel">how to read your lipid panel</a>, and if your LDL is flagged, see <a href="/conditions/high-cholesterol">high cholesterol</a>. Blood pressure counts as much as any lipid number; <a href="/conditions/high-blood-pressure">high blood pressure</a> explains the targets.

Free, no accountRead your blood testHave a lipid panel to read beside your calcium score? Read every line of it, free.Read my results

Can you lower your calcium score?

Calcium rarely goes away once it is in the artery wall, and on a <a href="/compounds/statins">statin</a> the score often goes up. A rising score on a statin can be a sign the plaque is stabilising rather than a sign the treatment is failing. Rishi Puri and colleagues pooled 8 intravascular ultrasound trials (studies that measure plaque from inside the artery with a tiny probe) and found that high-intensity statins shrank total plaque volume while increasing the calcium inside it ¹⁴. Statins appear to help turn soft plaque into denser, more stable plaque, and the Agatston method counts denser calcium at a higher weight.

The treatment the imaging studies tested

Strongest evidenceStatinsA prescription drug started and managed by a clinician. In pooled imaging trials, high-intensity statins reduced plaque volume while plaque calcium rose, so a higher score on treatment can reflect stabilising plaque.

For anyone already treated, the more useful things to follow over time are ApoB or LDL, blood pressure, blood sugar and smoking status, rather than the calcium score itself. For what the evidence says about supplements and the heart, see <a href="/supplements-for/heart-health">supplements for heart health</a>.

How often to repeat a calcium scan

Calcium score vs CT angiogram vs stress test

If you have chest pain, the right tests are a CT coronary angiogram or a stress test, chosen by your clinician. A screening calcium scan is the wrong tool.

Cost, preparation and the day itself

In the US a calcium scan usually costs roughly $100 to $400 self-pay, and prices vary by centre. Insurance often does not cover it as a screening test, so ask before booking. RadiologyInfo says you will usually be asked not to eat or drink and to avoid caffeine and smoking for four hours before the exam, to leave jewellery at home and to wear loose, comfortable clothing ¹. Results normally arrive within a few days. The radiologist may mention findings outside the heart, most often small lung nodules, which usually need only follow-up imaging.

Free, no accountDrop in your lab report and see every marker explained in plain words, placed on the body, against your lab's range. It's read on your device: nothing is uploaded and nothing is kept.

Read my results Download the app