Definition and Pathophysiology
Coronary artery calcium (CAC) scoring is a non-invasive method for detecting and quantifying calcified coronary atherosclerotic plaque. It is performed using a non-contrast, electrocardiographically gated computed tomography (CT) scan. Image acquisition generally requires a single breath-hold and does not require intravenous access, premedication, or special preparation.
The most widely used quantification method is the Agatston score, which incorporates both the area and radiographic density of coronary calcification. CAC therefore functions primarily as an imaging biomarker of coronary atherosclerotic burden rather than as a direct measure of luminal obstruction.
Calcified plaque is generally less likely to rupture than non-calcified, lipid-rich plaque. CAC nevertheless serves as a marker of the broader atherosclerotic process, including non-calcified plaques that are not directly visualized by calcium scoring. In contrast, coronary CT angiography (CCTA) can characterize both calcified and non-calcified plaque and can assess stenosis.
A major limitation is that CAC does not measure total plaque burden or stenosis severity directly. A patient may have little or no calcium despite clinically relevant non-calcified plaque, particularly in middle age. Conversely, a high CAC score indicates substantial atherosclerotic burden but does not, by itself, establish the presence or haemodynamic significance of a specific stenosis.
Clinical Role and Indications
CAC scoring is principally a risk-stratification tool for individuals without known clinical coronary artery disease, especially when conventional risk estimates leave uncertainty near a treatment decision threshold. It can move estimated cardiovascular risk upward or downward and may assist decisions concerning lipid-lowering therapy and broader preventive management.
The test is particularly relevant when the decision to initiate or intensify preventive therapy is uncertain. Prevention guidelines support its use in selected individuals at intermediate risk, rather than as a universal population-screening test. It may also be considered in selected lower-risk individuals with a family history of premature coronary artery disease.
CAC findings incidentally identified on a chest CT performed for another indication can also contribute to risk assessment. Visual reporting of coronary calcification using four categories—none, mild, moderate, or severe—is recommended when such findings are available. Further diagnostic imaging solely because calcified plaque is present in an asymptomatic individual is not supported by the available evidence described here.
Systematic screening of the general population for cardiovascular risk factors has not been shown to improve cardiovascular outcomes, although opportunistic assessment during clinical encounters improves detection of risk factors such as elevated blood pressure and lipid abnormalities. CAC should therefore be integrated with clinical assessment and established risk-estimation systems rather than used in isolation.
Test Performance and Acquisition
A contemporary CAC examination has several practical characteristics:
Non-contrast CT acquisition
ECG gating
A single breath-hold
No intravenous line
No premedication
No special preparation
Radiation exposure of approximately 1–1.5 mSv with contemporary techniques
The total CAC burden should be reported using the Agatston score. A complete report should ideally include:
Total Agatston score
Calcium score in each coronary vessel
Age-, sex-, and race-based percentile
Comparison with the expected score for a person of the same age and sex
CAC may also reveal extracoronary findings, including pericardial or aortic calcification, pericardial thickening, valvular calcification, and, in some cases, fatty liver disease.
Interpretation of the Agatston Score
The score should be interpreted both by its absolute value and in relation to age and sex. A score that is high for the patient’s demographic group confers greater risk than the same absolute score might imply in an older person. Conversely, absent or less-than-expected calcification may indicate lower risk than predicted by conventional risk factors.
Common CAC Categories
| Agatston score | Calcified plaque burden | Practical interpretation |
|---|---|---|
| 0 | Absent | No identified coronary calcification; associated with very low 10-year cardiovascular event risk, reported as <5% in the supplied classification |
| 1–9 | Minimal | Minimal atherosclerosis; associated with low 10-year cardiovascular event risk, reported as <10% |
| 10–99 | Mild | Mild coronary atherosclerosis; mild or minimal stenosis is likely |
| 100–299 | Moderate | Moderate calcific burden and increased cardiovascular risk |
| 300–999 | Severe | Extensive atherosclerotic burden; risk may approach that associated with secondary prevention |
| ≥1000 | Extreme | Very extensive calcification and markedly elevated risk |
An alternative classification describes scores of 101–400 as moderate and scores above 400 as extensive. In that framework, a score above 400 is associated with a high probability of at least one significant coronary stenosis and a significant risk of cardiovascular events over the subsequent decade. These categories should be viewed as interpretive aids rather than as direct anatomical definitions of obstructive disease.
CAC Score of Zero
A CAC score of zero is associated with very low cardiovascular risk in appropriately selected individuals and makes obstructive coronary disease less likely. It does not, however, exclude non-calcified plaque or eliminate the possibility of future events. CAC may be absent in middle-aged patients with soft, non-calcified plaque, including lesions capable of causing clinical events.
A zero score should therefore be interpreted in the context of age, symptoms, risk factors, and the clinical question. It is most useful as a negative risk marker in individuals without known coronary disease when the decision about preventive therapy is uncertain.
High CAC Scores
Higher CAC scores are associated with progressively greater cardiovascular risk. In asymptomatic populations, extensive calcification—particularly scores in the range of 300–1000—has been associated with mortality risk similar to that observed in secondary prevention populations. A markedly elevated score should prompt careful attention to modifiable risk factors and preventive treatment.
CAC does not, however, determine whether invasive angiography or revascularization is required. A high score may coexist with non-obstructive disease, while an individual with a low score may still have non-calcified obstructive plaque.
Prognostic Use
CAC improves cardiovascular risk discrimination and reclassification beyond conventional risk factors and risk scores. Its prognostic value has been demonstrated across racial and ethnic groups, and CAC strongly predicts all-cause mortality as well as cardiovascular events.
The relationship between CAC burden and risk is graded:
Individuals with no detectable calcium have very low estimated risk.
Minimal and mild calcification indicate the presence of coronary atherosclerosis but generally lower risk than moderate or extensive disease.
Moderate and severe calcification identify progressively increasing risk.
Very high scores may indicate risk comparable to that of established clinical atherosclerotic cardiovascular disease.
CAC therefore provides direct evidence of subclinical atherosclerosis, whereas conventional scores estimate risk from biological and clinical risk factors. Imaging can improve risk prediction and may increase adherence to lifestyle and pharmacological preventive interventions.
The prognostic value of CAC is not limited to a single coronary vessel. Total burden is important, but vessel-specific distribution and demographic percentiles add interpretive information.
Relationship to Plaque Biology and Coronary Events
CAC detects calcified plaque but not the full spectrum of coronary atherosclerosis. The lesions most likely to precipitate acute events may be non-calcified and lipid-rich, with thin fibrous caps. CCTA can identify these lesions and may demonstrate features associated with increased plaque vulnerability, including:
Low-attenuation plaque
Positive remodelling
Spotty calcification
Diffuse calcium or calcium sheets identified by CAC are biologically different from these high-risk plaque features. Consequently, a low or zero CAC score should not be interpreted as proof that the coronary arteries are free of clinically relevant plaque.
CCTA also demonstrates that a substantial proportion of coronary events occur in patients without severe obstructive disease. Non-obstructive plaque may therefore have important prognostic and therapeutic implications even when the stenosis is not severe.
CAC in Symptomatic Patients
CAC is primarily used for risk assessment in individuals without known coronary disease, but it may also have a role in selected patients with symptoms and low clinical risk. Very low CAC, particularly a score of zero, makes obstructive disease less likely and, in some patients with stable symptoms, may obviate further evaluation.
When diagnostic testing is indicated in symptomatic patients without known coronary disease, CCTA is generally preferred over CAC alone when the clinical objective is to assess the presence and extent of disease. CCTA can evaluate:
Non-calcified and calcified plaque
Coronary stenosis
Plaque composition
Ventricular function
CCTA is particularly useful in patients with intermediate to high risk and stable chest pain without known coronary disease, and as a first-line test in appropriate symptomatic patients. It has advantages over functional testing in adults younger than 65 years and when the suspicion of obstructive disease is lower.
CAC alone is insufficient when the clinical question concerns stenosis severity or lesion-specific ischaemia.
Comparison with Coronary CT Angiography
| Feature | CAC scoring | CCTA |
|---|---|---|
| Contrast | Not required | Required |
| Primary purpose | Quantification of calcified plaque and risk stratification | Assessment of plaque, stenosis, and coronary anatomy |
| Plaque detected | Calcified plaque | Calcified and non-calcified plaque |
| Stenosis assessment | Indirect and unreliable | Direct anatomical assessment |
| Preparation | Breath-hold; no intravenous access or premedication | Requires protocol-specific preparation and intravenous contrast |
| Best-established role | Asymptomatic individuals near preventive treatment thresholds | Symptomatic patients requiring assessment for coronary disease |
| Major limitation | Does not quantify total plaque or stenosis and may miss non-calcified plaque | Image quality may be limited by tachycardia, heavy calcification, atrial fibrillation, or coronary stents |
CCTA has a high negative predictive value for excluding significant coronary disease and can identify patients with no plaque or stenosis. It may also guide subsequent invasive testing and preventive therapy. In lesions of uncertain haemodynamic significance, fractional flow reserve derived from CT can provide lesion-specific physiological information; a normal result may help avoid unnecessary invasive angiography.
Biomarkers and Laboratory Findings
CAC is itself an imaging biomarker rather than a blood test. The supplied material identifies additional cardiovascular risk markers, including:
Persistently elevated high-sensitivity C-reactive protein: >2 mg/L
Elevated lipoprotein(a): >50 mg/dL or >105 nmol/L
These markers may contribute to overall risk assessment, but CAC should be interpreted alongside the complete cardiovascular risk profile rather than as a replacement for clinical and laboratory evaluation.
Risk-estimation algorithms such as SCORE2 and SCORE2-OP are intended for individuals without established clinical atherosclerotic cardiovascular disease who are not receiving lipid-lowering therapy. They should not be used to estimate risk in patients with existing ASCVD or to reassess risk using lipid measurements obtained after lipid-lowering treatment has begun.
Management According to CAC Findings
General Principles
CAC results should alter the intensity and clarity of preventive management rather than automatically trigger invasive investigation. Management should include attention to:
Lipid-lowering therapy
Diet
Physical activity
Smoking cessation
Blood pressure and other modifiable risk factors
Adherence to preventive treatment
The presence of CAC may improve motivation for lifestyle and pharmacological interventions, particularly in patients who previously lacked motivation despite having risk factors.
Lipid-Lowering Therapy
CAC can support initiation or intensification of lipid-lowering therapy when the estimated risk is near a treatment threshold. The intensity of LDL-cholesterol reduction remains determined by the patient’s overall cardiovascular risk and baseline untreated LDL-cholesterol level.
CAC should be interpreted cautiously in patients already receiving statins. Statin therapy can reduce lipid-rich plaque while increasing its conversion to calcified plaque; therefore, an increase in CAC during treatment does not necessarily indicate treatment failure or plaque destabilization.
Antithrombotic Therapy
CAC may potentially assist decisions about primary-prevention aspirin, but randomized evidence is lacking. CAC should not be regarded as an independent indication for antithrombotic treatment based solely on the score.
Revascularization and Invasive Testing
CAC scoring alone should not determine revascularization. In stable coronary disease, the presence of ischaemia does not necessarily imply that an initial revascularization strategy improves outcomes over medical therapy. The decision to proceed to invasive angiography or revascularization should depend on the clinical presentation, anatomical findings, symptoms, and the relevant diagnostic assessment.
In patients with symptoms, CCTA may better define disease extent and guide invasive angiography. CCTA can also exclude significant left-main disease before a medical strategy is pursued in selected patients with stable angina.
Repeat Testing and Follow-Up
Routine repeat CAC testing has minimal, if any, role once lipid-lowering therapy has been initiated. This is partly because statins may increase coronary calcification while stabilizing plaque, making serial score changes difficult to interpret as treatment response.
Follow-up should instead focus on:
Implementation and adherence to preventive treatment
Control of modifiable risk factors
Reassessment of clinical symptoms
Appropriate use of established risk-estimation methods in eligible untreated individuals
Further anatomical or functional testing only when symptoms or clinical circumstances warrant it
An incidentally detected CAC finding on a previous non-gated chest CT should be incorporated into cardiovascular risk assessment and preventive management. Visual grading as none, mild, moderate, or severe is recommended when formal scoring is unavailable.
Guideline Recommendations
The recommendations supplied for asymptomatic individuals are summarized below.
| Recommendation | Class | Level |
|---|---|---|
| Opportunistic screening for cardiovascular risk factors and estimation of future cardiovascular risk using systems such as SCORE2 and SCORE-OP is recommended to identify high-risk individuals and guide treatment decisions | I | C |
| When CAC is visible on a prior chest CT, its use to improve risk stratification and guide treatment of modifiable risk factors should be considered | IIa | C |
| CAC scoring may be considered to improve risk classification when a patient is near a treatment decision threshold | IIb | C |
| Carotid ultrasound may be considered when CAC is unavailable or unsuitable to detect atherosclerotic disease and refine risk classification near a treatment threshold | IIb | B |
The overall guideline position is that CAC is useful when uncertainty remains about cardiovascular risk or the role of lipid-lowering therapy, but it is not recommended as a broad screening test for the general population.
Limitations and Practical Pitfalls
CAC Is Not a Stenosis Test
A high score indicates atherosclerotic burden but does not establish the severity of luminal obstruction. Conversely, a low score cannot exclude non-calcified plaque or significant stenosis, particularly in younger patients.
Non-Calcified Plaque May Be Missed
CAC detects only calcified plaque. It may miss lipid-rich, non-calcified lesions that are capable of producing acute coronary events. CCTA is required when plaque composition or stenosis must be evaluated.
Age and Sex Matter
The same absolute score may represent markedly different percentile rankings in different patients. Reports should therefore include age-, sex-, and race-based percentiles and indicate whether the score is greater or less than expected for the individual’s demographic group.
Statin Therapy Complicates Serial Interpretation
Statins may promote plaque stabilization through reduction of lipid-rich plaque and increased calcification. Serial CAC progression after treatment initiation should therefore not be interpreted simplistically as worsening atherosclerosis.
Radiation and Resource Considerations
Although contemporary radiation exposure is low, approximately 1–1.5 mSv, the availability, cost-effectiveness, and local healthcare context should be considered before implementing large-scale CAC scanning.
Incidental Findings
CAC scans may reveal non-coronary abnormalities, including aortic or valvular calcification, pericardial abnormalities, or fatty liver disease. These findings may require separate clinical consideration.
Prognosis and Clinical Follow-Up
CAC provides a graded estimate of future cardiovascular risk and is especially valuable in asymptomatic individuals whose conventional risk estimate is uncertain. A score of zero generally identifies a very low-risk state, whereas extensive or extreme calcification identifies a substantially higher-risk state, in some cases comparable to secondary prevention.
The score should be used to refine preventive treatment, not to replace clinical assessment. Long-term management is determined by the combination of CAC burden, age, sex, established risk factors, symptoms, lipid profile, blood pressure, smoking status, diabetes status, and the presence or absence of clinical ASCVD.
After a CAC result has been incorporated into preventive decision-making, follow-up should emphasize sustained risk-factor modification and treatment adherence. Repeat CAC scanning is generally of limited utility after lipid-lowering therapy has started. New or changing symptoms should prompt reassessment using an appropriate diagnostic pathway, often including CCTA or functional testing rather than repeat calcium scoring alone.
