CAC Score (Coronary Artery Calcium): When to Order This Test

What a CAC Score Actually Measures

A coronary artery calcium (CAC) score quantifies the total burden of calcified atherosclerotic plaque in the coronary arteries using a non-contrast, ECG-gated CT scan. The result is reported as an Agatston score, named after Arthur Agatston, who developed the method in 1990. Higher numbers mean more plaque.

The Agatston Scoring Method

The Agatston method assigns a density score to each calcified lesion based on its peak CT attenuation (measured in Hounsfield units) and multiplies that by the lesion area [1]. Individual lesion scores are summed across all four major coronary territories: left main, left anterior descending, circumflex, and right coronary artery. A score of zero means no detectable calcified plaque. A score above 300 indicates extensive coronary atherosclerosis.

What CAC Does Not Detect

The test cannot identify soft (non-calcified) plaque, which may still rupture and cause acute coronary events. It also does not measure the degree of luminal stenosis. A patient with a CAC of zero can still have non-calcified plaque, though the short-term event risk remains very low. The Multi-Ethnic Study of Atherosclerosis (MESA) found that among 3,415 participants with a CAC score of zero, the 10-year coronary event rate was only 1.1% [2].

How It Compares to Other Cardiac Tests

Unlike a stress test, which evaluates functional blood flow, the CAC scan provides an anatomical snapshot of plaque accumulation. It is not a replacement for coronary CT angiography (CCTA), which uses contrast dye and can visualize both calcified and non-calcified lesions. The CAC score is a screening and risk-stratification tool, not a diagnostic test for active chest pain [3].

Who Should Get a CAC Score

The 2019 ACC/AHA Guideline on the Primary Prevention of Cardiovascular Disease gives CAC scoring a Class IIa recommendation for adults aged 40 to 75 whose 10-year atherosclerotic cardiovascular disease (ASCVD) risk falls between 7.5% and 19.9%, particularly when the statin decision is uncertain [4]. This is the test's sweet spot.

The Intermediate-Risk Patient

Intermediate risk means a calculated 10-year ASCVD probability of 7.5% to 19.9% using the Pooled Cohort Equations. These patients sit in a gray zone. Some will benefit from early statin therapy; others will take a medication for decades with minimal gain. The CAC score breaks the tie. The 2019 guidelines state: "If the coronary artery calcium score is zero, it is reasonable to withhold statin therapy and reassess in 5 to 10 years, as long as higher-risk conditions are absent" [4].

Borderline-Risk Patients (5% to 7.5%)

The guidelines also support CAC testing in borderline-risk adults (5% to <7.5% 10-year risk) when "risk-enhancing factors" are present [4]. Risk enhancers include a family history of premature ASCVD, South Asian ancestry, metabolic syndrome, chronic kidney disease, chronic inflammatory conditions (rheumatoid arthritis, psoriasis, HIV), history of preeclampsia or premature menopause, and persistently elevated triglycerides above 175 mg/dL.

Who Should Not Get This Test

CAC scoring is not recommended for low-risk adults (10-year ASCVD risk <5%) or for patients who already qualify for high-intensity statin therapy based on clinical ASCVD, LDL-C of 190 mg/dL or higher, or diabetes with multiple risk factors [4]. In these groups, the result will not change management. The test is also not appropriate for symptomatic patients with active chest pain; those patients need diagnostic evaluation, not screening.

Understanding Your CAC Score Results

The Agatston score falls into well-defined categories that map directly to clinical action. The MESA cohort study (N=6,814) established the prognostic value of each tier over a median follow-up of 11.1 years [2].

Score of Zero

A CAC of zero is the single most powerful negative risk marker in preventive cardiology. In MESA, participants with CAC = 0 had an annualized coronary heart disease event rate of 0.11% [2]. Dr. Michael Blaha of Johns Hopkins has stated: "A zero calcium score is the most powerful negative risk factor we have ever identified in cardiovascular medicine" [5]. For intermediate-risk patients, a zero score can reasonably delay statin initiation for 5 to 10 years.

Score of 1 to 99

Mild plaque is present. The 10-year CHD event rate in MESA for this group was approximately 3.9% [2]. A statin conversation is appropriate, and lifestyle modifications (dietary changes, exercise, smoking cessation) should be started or intensified. The presence of any calcium confirms subclinical atherosclerosis exists.

Score of 100 to 299

Moderate plaque burden. The MESA 10-year event rate rose to roughly 7.2% in this range [2]. Statin therapy is recommended for most patients in this category, along with aspirin consideration in select cases and aggressive blood pressure management. This score often reclassifies patients from "uncertain" to "treat."

Score of 300 or Higher

Extensive calcified plaque. Patients with scores above 300 carry a 10-year CHD event rate exceeding 13% in MESA data [2]. High-intensity statin therapy is indicated. Additional workup (stress testing, CCTA) may be considered depending on symptoms and clinical context. A score above 1,000 is sometimes called "very high" and warrants the most aggressive preventive strategy available.

Age and Sex Percentiles

Raw Agatston scores should be interpreted alongside age-, sex-, and ethnicity-based percentiles from the MESA database. A score of 50 in a 45-year-old man places him well above the 75th percentile for his demographic, while the same score in a 70-year-old woman may fall near the median [6]. The MESA CAC calculator (available through the MESA-NHLBI website) converts raw scores to percentiles.

How the CAC Score Changes Cardiovascular Risk Management

The principal value of CAC scoring lies in reclassification. A 2018 analysis from the MESA investigators found that adding CAC to the Pooled Cohort Equations correctly reclassified 50% of intermediate-risk adults [7]. Half of the patients previously labeled "intermediate risk" were moved to either low risk (CAC = 0) or high risk (CAC above 100), directly changing their treatment plan.

Statin Decision-Making

The most common clinical use is resolving statin ambivalence. A 55-year-old woman with a 10-year ASCVD risk of 10%, no diabetes, and an LDL-C of 145 mg/dL sits squarely in the "maybe statin" category. If her CAC returns zero, deferral is reasonable. If it returns 150, a moderate-intensity statin is appropriate. The 2019 ACC/AHA guidelines explicitly endorse this approach [4].

Aspirin Therapy

The 2019 guidelines weakened the recommendation for primary prevention aspirin in most adults. A CAC score above 100 is one of the few scenarios where low-dose aspirin may still be considered in primary prevention for patients aged 40 to 70 who are not at increased bleeding risk [4]. The USPSTF issued a Grade C recommendation (small net benefit) for aspirin in adults aged 40 to 59 with 10% or greater 10-year ASCVD risk, and recommended against routine initiation in adults 60 and older [8].

Motivating Lifestyle Change

Seeing calcium on a scan changes patient behavior. A study published in the American Journal of Preventive Medicine (N=2,039) found that patients who received their CAC results were significantly more likely to initiate statin therapy (OR 2.5, 95% CI 1.4 to 4.3) and increase physical activity compared to controls who received risk factor counseling alone [9]. The visual confirmation of disease can be more persuasive than a percentage on a calculator.

What the Test Involves

The scan itself is fast and non-invasive. No fasting, no IV contrast, and no special preparation.

Procedure Details

The patient lies on the CT scanner table. ECG leads are placed on the chest to synchronize imaging with the heartbeat. The scan acquires images during a single breath-hold of about 10 seconds. Total time in the scanner room is typically under 10 minutes. Results are usually available within 24 to 48 hours.

Radiation Exposure

The effective radiation dose is approximately 1 mSv, comparable to a two-view screening mammogram or roughly 4 months of natural background radiation [3]. This is well below the threshold for clinical concern in a one-time screening context.

Cost and Insurance

Most insurers do not cover CAC scanning because it remains classified as a screening (not diagnostic) test. Out-of-pocket cost ranges from $75 to $300 depending on the facility and region. Some health systems offer self-pay cardiac CT packages that include the CAC scan. Medicare does not cover screening CAC scans as of 2026.

Normal CAC Score Ranges by Age and Sex

There is no single "normal" CAC value. Coronary calcium increases with age in healthy populations. What matters clinically is the score relative to peers.

Population-Based Norms

Data from MESA (N=6,814 participants, free of clinical cardiovascular disease at enrollment) provide the reference standard [6]. At age 55, the median CAC score for white men is approximately 10 to 30, while for white women the median is 0. By age 75, median scores rise to 200 to 400 for men and 50 to 150 for women. Black participants tend to have lower CAC scores than white participants at every age, despite similar or higher rates of clinical cardiovascular events, a finding known as the "CAC paradox" [10].

The 75th Percentile Threshold

A score above the 75th percentile for age, sex, and ethnicity signals disproportionate plaque accumulation and confers additional risk beyond the raw number. The ACC/AHA guidelines note that a CAC score at or above the 75th percentile favors statin therapy even when the absolute score is modest [4].

Can You Lower a CAC Score?

This question comes up frequently. The honest answer: probably not, and that is acceptable.

What Statins Do to CAC

Statins slow plaque progression but may actually increase CAC scores over time. The St. Francis Heart Study and the MESA follow-up data both showed that statin-treated patients had slower growth in total plaque volume but similar or slightly higher rates of calcium deposition [11]. This happens because statins stabilize soft plaque by promoting calcification of the lipid core, essentially converting dangerous soft plaque into stable calcified plaque. A rising CAC score on statin therapy does not mean treatment is failing.

Lifestyle Factors

No lifestyle intervention has been shown to reverse established coronary calcification. Exercise, dietary changes, and smoking cessation reduce overall cardiovascular risk and slow new plaque formation, but calcium, once deposited, does not dissolve. The American Heart Association notes that the goal is risk reduction, not score reduction [12].

Why Rescreening Is Generally Not Recommended

Because CAC scores almost never decrease and therapeutic success does not correlate with score changes, the 2019 ACC/AHA guidelines do not recommend routine repeat CAC scanning [4]. Repeat testing may be considered on a case-by-case basis (for example, a patient with CAC = 0 who is reassessed after 5 to 10 years), but serial tracking of scores to guide therapy adjustments lacks evidence.

Special Populations and Considerations

Young Adults (Under 40)

CAC screening is not routinely recommended for adults under 40. The prevalence of detectable calcium is low in this age group, and the Pooled Cohort Equations are not validated below age 40 [4]. Exceptions may include individuals with severe familial hypercholesterolemia or a very strong family history of premature ASCVD.

Adults Over 75

The guidelines do not provide strong guidance on CAC scoring in adults over 75 because most people in this age group already have some degree of coronary calcification. Clinical judgment should drive statin decisions in this population, and CAC is less likely to reclassify risk meaningfully.

Women

Women develop coronary calcification approximately 10 to 15 years later than men. A CAC score of zero is more common in women at any given age, and its negative predictive value is equally strong. However, women with detectable CAC face event rates comparable to men with similar scores [2]. The test is particularly useful in perimenopausal and postmenopausal women with intermediate risk scores, where traditional risk calculators may underestimate true risk.

South Asian Ancestry

The ACC/AHA guidelines list South Asian ancestry as a risk-enhancing factor [4]. CAC scoring may be appropriate at lower calculated risk thresholds in this population due to higher observed rates of premature ASCVD relative to risk calculator predictions.

How to Order a CAC Score

Ordering is straightforward. A clinician (physician, NP, or PA) places an order for a non-contrast cardiac CT for coronary artery calcium scoring. No prior authorization is typically needed because the test is self-pay in most cases.

Preparation

No fasting required. No IV line needed. Patients should avoid caffeine for 4 hours before the scan if the facility requests it (caffeine can raise heart rate, reducing image quality). Beta-blockers are not needed for CAC-only scans, unlike coronary CT angiography.

Reading the Report

The report will include the total Agatston score, individual vessel scores (LAD, LCx, RCA, left main), and often the age/sex/ethnicity percentile. The ordering clinician should review the result in the context of the patient's full risk profile, not in isolation. A 2022 expert consensus from the Society of Cardiovascular Computed Tomography (SCCT) recommends that all CAC reports include percentile ranking alongside the raw Agatston score [13].

The AHA/ACC 2019 guidelines summarize the clinical action framework: "For patients in whom, after quantitative risk estimation, a risk-based treatment decision is uncertain, it is reasonable to measure a CAC score to guide clinician-patient risk discussion" [4]. If the score returns as zero, document it and reassess in 5 to 10 years. If positive, treat the modifiable risk factors with the intensity that the score category warrants.