Most cardiovascular risk assessments are built on inference. Cholesterol numbers, blood pressure readings, family history — these are all proxies that help estimate the probability of future arterial disease. They tell us what might be happening inside your arteries.
The coronary artery calcium (CAC) score tells us what is happening. It is a low-radiation CT scan that directly visualizes calcified plaque in the walls of the coronary arteries — the vessels that supply the heart muscle. A single, non-contrast scan performed in under 10 minutes produces a score that is one of the most powerful predictors of cardiovascular events available in clinical medicine.
And yet the majority of adults who would benefit from it have never had one. This post explains what the test measures, how to interpret the results, and who should get it.
What the CAC Score Actually Measures
The Agatston score — the standard CAC scoring method — quantifies the total calcium burden in the coronary arteries by measuring the area and density of each calcified lesion detected on CT. The result is expressed as a single number with no units. A score of zero means no calcified plaque was detected. Higher numbers indicate greater plaque burden.
It is important to understand what calcium in the arterial wall represents. Calcification is a late-stage process in atherosclerosis — it occurs after lipid-rich plaque has formed and begun to evolve over years or decades. A positive CAC score is evidence that atherosclerosis is present and has been progressing. It is not a transient finding; calcified plaque does not resolve spontaneously.
The scan does not detect all plaque — specifically, soft or non-calcified plaque is invisible to the CAC scan. This means a CAC of 0 does not guarantee zero atherosclerosis, particularly in younger patients or those with very recent disease onset. However, it does mean that the cumulative plaque burden is low enough that no calcification has yet occurred — a finding with very strong prognostic value.
How to Interpret Your Score
CAC = 0
No calcified plaque detected. 10-year MACE rate below 1% in most studies. Strong warrant to defer statin therapy in borderline-risk patients.
CAC 1–99
Mild plaque burden. Atherosclerosis is present and confirmed. Treatment decisions depend on total risk context and percentile ranking.
CAC 100–399
Moderate plaque burden. Strong indication for statin therapy, blood pressure optimization, and comprehensive risk factor management.
CAC ≥ 400
High plaque burden. Aggressive risk factor management. High-intensity statin, aspirin consideration, and close follow-up.
Raw score alone does not tell the full story. The MESA (Multi-Ethnic Study of Atherosclerosis) percentile calculator compares your score to others of the same age, sex, and ethnicity — and this percentile context can be clinically decisive. A 45-year-old man with a CAC of 100 is in the 90th percentile for his age and sex, which carries very different implications than a 70-year-old with the same score who may be at the 50th percentile.
The Extraordinary Power of a Zero Score
A CAC score of 0 is one of the most reassuring findings in all of preventive cardiology. The MESA trial, following over 6,500 individuals over 10 years, demonstrated that patients with a CAC of 0 had cardiovascular event rates below 1% — even among those with elevated LDL, blood pressure, or other traditional risk factors.
For patients in the "borderline" risk zone who are weighing whether to start a statin, a CAC of 0 is often compelling evidence to defer pharmacotherapy and focus on lifestyle optimization. This is a conversation that standard risk calculators simply cannot facilitate. The 10-year ASCVD risk score may say 10% — the CAC says zero calcified plaque is present in your arteries. Those are very different clinical messages.
The Statin Deferral Decision
Current ACC/AHA guidelines explicitly support using CAC = 0 as a reason to withhold statin therapy in borderline-risk patients who prefer to defer pharmacotherapy. This is not a fringe position — it is guideline-endorsed shared decision-making supported by Level A evidence.What a High Score Demands
Conversely, a high CAC score — particularly in the 75th percentile or above for age and sex — demands aggressive management even when traditional risk factors appear only mildly elevated. Studies consistently show event rates in high-CAC patients that justify:
- High-intensity statin therapy with an LDL target well below standard thresholds (often below 55 mg/dL)
- ApoB target below 65–70 mg/dL
- Strict blood pressure control (systolic below 120–125 mmHg in appropriate candidates)
- Daily low-dose aspirin consideration in patients without bleeding contraindications
- Aggressive lifestyle intervention as urgency — not just good practice
- More frequent clinical monitoring and earlier repeat imaging in select cases
CAC Score vs. Stress Testing: An Important Distinction
Patients sometimes confuse the CAC score with a stress test. These answer completely different clinical questions and are not interchangeable.
The CAC score is a screening tool for asymptomatic individuals to quantify atherosclerotic plaque burden and guide primary prevention. It does not detect whether any artery is significantly narrowed or whether blood flow to the heart is impaired.
Stress testing — exercise ECG, nuclear stress, or stress echocardiogram — evaluates for flow-limiting coronary disease in patients with symptoms: exertional chest pain or pressure, shortness of breath with exertion, unexplained fatigue, or palpitations. It is a diagnostic tool, not a screening tool.
A patient with a very high CAC score but no symptoms does not typically need a stress test. Their management is intensified medical therapy — not invasive evaluation unless symptoms develop.
The Procedure Itself
The CAC scan requires no contrast dye, no treadmill, and no special preparation. You lie in a CT scanner for approximately 10–15 minutes while images are acquired during a series of short breath-holds. The scan is fast, painless, and delivers a radiation dose roughly equivalent to a mammogram — substantially lower than a standard chest CT with contrast.
CAC Scan: Practical Details
Insurance coverage for CAC scoring in asymptomatic individuals is variable. Many patients pay out of pocket, and at $75–$250 at most imaging centers, it is among the most cost-effective tests in preventive medicine relative to the clinical information it provides.
Who Should Get a CAC Score
Current ACC/AHA guidelines recommend CAC scoring for adults aged 40–75 at intermediate ASCVD risk where the treatment decision remains uncertain. Many preventive cardiologists, myself included, apply it more broadly — for any motivated patient who wants a precise understanding of their actual arterial health rather than a probability estimate.
Strong indications include:
- Adults 40–75 with any cardiovascular risk factors who are uncertain whether to start statin therapy
- Strong family history of premature cardiovascular disease (first-degree relative with MI or stroke before age 55 in men or 65 in women)
- Borderline 10-year ASCVD risk (7.5–20%) where risk enhancers are present but the treatment decision remains unclear
- Patients who prefer to defer statin therapy and want objective data to inform that decision
- Patients with apparently normal lipids and metabolic markers who want direct arterial assessment
- Younger patients (40–50) with significant family history, diabetes, or early-onset risk factors
Who Should NOT Get a CAC Score
The CAC scan is not appropriate for patients with established cardiovascular disease (who already have a known indication for aggressive therapy), those who are already committed to statin therapy regardless of results, or patients under 40 without compelling risk factors. It is most valuable when the result can change management.Women and the CAC Score
Women are systematically underscreened and undertreated for cardiovascular disease. The CAC score is particularly valuable in women because traditional risk calculators consistently underestimate risk in women who develop atherosclerosis — often because they present later in life and with different risk factor profiles than men.
Women with a positive CAC score, even modest ones, warrant the same aggressive risk management as men with equivalent scores. A 58-year-old woman with a CAC of 80 and "borderline" traditional risk factors has objective evidence of atherosclerosis and should be managed accordingly — not reassured based on population-level statistics that routinely underestimate her individual risk.
ElinMed's Approach to CAC Scoring
For patients at ElinMed who fall into borderline or intermediate risk categories — or for any patient who wants to understand their arterial health directly — I discuss CAC scoring as part of the preventive cardiology assessment. I help coordinate the scan, interpret the result in the context of your full risk profile, and integrate it into a comprehensive prevention plan. A number without context is not a plan.Know Your Coronary Health
A risk calculator gives you a probability. A CAC score gives you a direct view of your arteries. At ElinMed, we help you decide whether a CAC scan is right for you and build a prevention strategy around the results.
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