A coronary artery calcium (CAC) scan uses low-dose CT to detect and measure calcified plaque in coronary arteries. Calcium deposits indicate atherosclerosis (plaque buildup). The scan produces a CAC score (Agatston score) reflecting the amount of calcium. Higher scores indicate more atherosclerosis and higher cardiovascular risk. Procedure: lie on CT table; brief breath holds; no contrast typically needed; 10-15 minutes; low radiation dose (about 1 mSv — similar to mammogram or one year of natural background). Useful for adults with intermediate cardiovascular risk to refine assessment. Agatston score categories: 0 (no calcified plaque, very low 10-year CV risk, very reassuring), 1-10 (minimal calcification, low risk), 11-100 (mild calcification, intermediate risk), 101-400 (moderate calcification, moderate to high risk), over 400 (severe calcification, high risk). Why adults with diabetes might consider CAC scan: diabetes alone is “risk-enhancing” but CAC provides personalized assessment; CAC 0 in adults with diabetes shows much lower CV risk than diabetes alone would suggest (may modify treatment intensity); CAC over 100 confirms high risk; adults at borderline cardiovascular risk especially; adults uncertain about statin therapy; family history of premature heart disease + diabetes; young adults with diabetes evaluating long-term risk. ACC/AHA 2018 guidelines recommend CAC for selected adults with intermediate CV risk to refine decision on statin therapy. Limitations: doesn’t detect non-calcified (soft) plaque (which can also cause heart attacks), doesn’t assess stenosis severity (calcium present but degree of narrowing unclear without contrast), cost ($100-500 out of pocket, insurance coverage variable), radiation exposure (low but not zero), incidental findings may require further workup, not replacement for clinical judgment, annual CAC not appropriate (scores change slowly; repeat in 5-10 years if needed).
CAC Score Interpretation
| CAC Score | Interpretation | 10-Year CV Risk |
|---|---|---|
| 0 | No calcified plaque | Very low (under 1% per year) |
| 1-10 | Minimal | Low |
| 11-100 | Mild plaque | Intermediate |
| 101-400 | Moderate plaque | Moderate to high |
| over 400 | Severe plaque | High |
| over 1000 | Extensive | Very high |
CAC in Diabetes Decision-Making
- Diabetes alone is “risk-enhancing factor” per ACC/AHA guidelines.
- CAC 0 in adults with diabetes — much lower CV risk than estimated by diabetes alone.
- May support holding statin therapy in some borderline situations.
- CAC over 100 confirms high CV risk; supports aggressive intervention.
- Helps individualize statin therapy decisions.
- Better than estimated risk for many adults.
- Not appropriate for very low risk (waste) or very high risk (treatment already indicated).
- Best for “intermediate” risk adults seeking clarification.
When CAC Might Be Indicated
- Adults with intermediate cardiovascular risk (5-20% 10-year risk).
- Adults uncertain about statin therapy.
- Family history of premature heart disease.
- Young or middle-aged adults wanting personalized assessment.
- Adults with one risk factor (like diabetes alone) at borderline.
- Decision-aid for cardiovascular preventive therapy.
- Patient preference for objective evidence.
- Not indicated: very low risk, very high risk, established CV disease, recent acute coronary syndrome.
Procedure and Results
- Lie on CT scanner table.
- EKG leads attached (gates to heart rhythm).
- Brief breath holds during scan.
- 10-15 minutes total.
- No IV contrast typically required.
- Low radiation dose (1 mSv — similar to mammogram).
- Results: Agatston score for each coronary artery and total.
- Cardiologist review.
- Discuss results with primary care or cardiologist.
- Score doesn’t change rapidly; repeat in 5-10 years if needed.
Limitations
- Doesn’t detect non-calcified plaque.
- Doesn’t measure stenosis severity.
- Younger adults may have CAC 0 with significant soft plaque.
- Doesn’t replace clinical judgment.
- Cost may not be covered by insurance.
- Radiation exposure (small).
- Incidental findings on chest CT.
- Not appropriate for very low or very high risk adults.
- One snapshot in time.
The Bottom Line
A coronary artery calcium (CAC) scan uses low-dose CT to detect and measure calcified plaque in coronary arteries. Calcium deposits indicate atherosclerosis (plaque buildup). The scan produces a CAC score (Agatston score) reflecting the amount of calcium — higher scores indicate more atherosclerosis and higher cardiovascular risk. Procedure: lie on CT table; brief breath holds; no contrast typically needed; 10-15 minutes; low radiation dose (about 1 mSv — similar to mammogram). Useful for adults with intermediate cardiovascular risk to refine assessment. Agatston score categories: 0 (no calcified plaque, very low 10-year CV risk under 1% per year, very reassuring), 1-10 (minimal, low risk), 11-100 (mild plaque, intermediate risk), 101-400 (moderate plaque, moderate to high risk), over 400 (severe plaque, high risk), over 1000 (extensive, very high). Score 0 in middle age provides strong reassurance about CV risk. High scores indicate need for aggressive cardiovascular risk reduction. Why adults with diabetes might consider CAC scan: diabetes alone is “risk-enhancing factor” per ACC/AHA guidelines but CAC provides personalized assessment; CAC 0 in adults with diabetes shows much lower CV risk than diabetes alone would suggest (may modify treatment intensity); CAC over 100 confirms high risk; helps individualize statin therapy decisions; better than estimated risk for many adults. ACC/AHA 2018 guidelines recommend CAC for selected adults with intermediate CV risk to refine decision on statin therapy. Not appropriate for very low risk (waste) or very high risk (treatment already indicated). Best for intermediate risk adults seeking clarification. When indicated: adults with intermediate cardiovascular risk (5-20% 10-year), uncertain about statin therapy, family history of premature heart disease, young or middle-aged adults wanting personalized assessment, decision-aid for preventive therapy. Limitations: doesn’t detect non-calcified (soft) plaque which can also cause heart attacks, doesn’t assess stenosis severity, cost typically $100-500 out of pocket (insurance variable), radiation exposure (low but not zero), incidental findings may require further workup, not replacement for clinical judgment, younger adults may have CAC 0 with significant soft plaque. Annual CAC not appropriate — scores change slowly; repeat in 5-10 years if needed. For adults with type 2 diabetes at intermediate cardiovascular risk seeking personalized assessment to guide treatment intensity, CAC scan provides valuable additional information beyond standard risk calculators. See our broader diabetes heart attack risk guide for context.
