Coronary Calcium CT: Purpose, Indications, and Contrast Use
A coronary calcium CT is a non-contrast CT scan that quantifies calcification in coronary arteries to assess atherosclerotic plaque burden and predict cardiovascular risk; it is primarily indicated for asymptomatic individuals with intermediate cardiovascular risk (10-20% 10-year risk) and does not require contrast. 1, 2
What is a Coronary Calcium CT?
- A coronary calcium CT (also called coronary artery calcium scoring or CAC) is performed using ECG-gated non-contrast CT of the heart to quantify calcification in coronary arteries
- It provides a direct measurement of atherosclerotic plaque burden, reported as an Agatston score
- The score is calculated by multiplying the density of the plaque (in Hounsfield units) by the area of the plaque
- Unlike coronary CT angiography (CCTA), calcium scoring does NOT use contrast 1
Who Needs a Coronary Calcium CT?
Appropriate Candidates:
Asymptomatic individuals with intermediate cardiovascular risk:
Specific low-risk patients:
Risk assessment refinement:
- When the decision to initiate statin therapy is uncertain 3
- To guide intensity of preventive interventions
Not Appropriate For:
- High-risk patients who already qualify for intensive preventive therapy
- Very low-risk patients without additional risk factors
- Symptomatic patients with high probability of CAD who should proceed directly to functional testing or coronary angiography
- Repeat testing in patients who have already had coronary calcium scoring 1
Is Coronary Calcium CT Done With Contrast?
No, coronary calcium CT is performed WITHOUT contrast. 1
- The calcium scoring protocol specifically requires non-contrast imaging to accurately identify and quantify calcification
- Contrast would obscure calcium deposits and invalidate the scoring system
- If visualization of coronary lumen, stenosis, or non-calcified plaque is needed, a separate coronary CT angiography (CCTA) with contrast would be performed
Coronary Calcium CT vs. Coronary CT Angiography
| Feature | Coronary Calcium CT | Coronary CT Angiography |
|---|---|---|
| Contrast | No contrast used | Requires IV contrast |
| What it shows | Only calcified plaque | Both calcified and non-calcified plaque, luminal stenosis |
| Radiation dose | Lower (typically ~1 mSv) | Higher (varies by protocol) |
| Primary use | Risk stratification | Diagnosis of coronary stenosis |
Clinical Implications of Calcium Scores
CAC = 0: Very low risk of future cardiovascular events and obstructive CAD
CAC = 1-100: Mild atherosclerotic plaque burden
- Indicates presence of CAD but low likelihood of significant stenosis
CAC = 101-400: Moderate atherosclerotic plaque burden
- Increased risk of cardiovascular events
CAC > 400: Severe atherosclerotic plaque burden
- High risk of cardiovascular events
- May indicate need for further testing
Important Considerations
- CAC scoring is not site-specific for luminal obstruction
- In symptomatic patients, a zero calcium score has excellent negative predictive value but does not completely exclude non-calcified plaque
- Extensive coronary calcification (score >800) may limit the diagnostic accuracy of subsequent CCTA if performed 1, 4
- In younger patients (<60 years), the value of CAC as a filter test prior to CCTA is limited 4
Pitfalls to Avoid
- Don't use CAC for screening in very low-risk populations
- Don't repeat CAC testing at short intervals (typically not more frequently than every 5 years)
- Don't rely solely on CAC in symptomatic patients with high clinical suspicion of CAD
- Don't confuse CAC (non-contrast) with CCTA (contrast-enhanced) when ordering the test
By understanding the appropriate use of coronary calcium CT, clinicians can better stratify cardiovascular risk and guide preventive interventions in selected patient populations.