When should a CT (Computed Tomography) calcium score be checked in adults with intermediate risk factors for cardiovascular disease, such as hypertension, high cholesterol, diabetes, or a family history of early coronary artery disease?

When to Check CT Calcium Score

CT calcium scoring should be checked in asymptomatic adults aged 40-75 years with intermediate cardiovascular risk (7.5-20% 10-year ASCVD risk) when the decision about statin therapy remains uncertain after initial risk assessment. 1

Primary Indications

Intermediate-Risk Patients (Class IIa Recommendation)

• Order CAC scoring for asymptomatic adults with 10-20% 10-year ASCVD risk where preventive treatment decisions are genuinely uncertain. 2, 1
• This represents the strongest evidence-based indication, with measurement of CAC being reasonable for cardiovascular risk assessment in this population. 2
• Age requirements: minimum 40 years for men and 50 years for women due to low prevalence of detectable calcium in younger individuals. 2, 3

Borderline-Risk Patients (Class IIb Recommendation)

• Consider CAC scoring in adults with 5-7.5% 10-year ASCVD risk who have specific risk-enhancing factors. 1
• Risk-enhancing factors include:
  • Family history of premature CAD 3, 1
  • Persistently elevated LDL-C 1
  • Chronic kidney disease 1
  • Elevated lipoprotein(a) >125 nmol/L (50 mg/dL) 3
  • Metabolic syndrome 3
  • Chronic inflammatory conditions 3

Special Populations

• Younger diabetic patients may warrant CAC scoring: Type 1 diabetes <35 years or Type 2 diabetes <50 years with diabetes duration <10 years and no other risk factors. 1
• High-risk patients who refuse recommended statin therapy, as CAC >100 may motivate adherence. 1

When NOT to Order CAC Scoring (Class III: No Benefit)

Low-Risk Patients

• Do not order CAC in patients with <5% 10-year ASCVD risk without risk-enhancing factors. 2, 4
• The test provides no actionable information that changes management in truly low-risk individuals. 3
• Even when CAC is detected in low-risk patients, absolute risk remains low enough that aggressive interventions are not warranted. 3

Symptomatic Patients

• Never order CAC scoring in symptomatic patients with chest pain or known CAD. 3
• CAC=0 does not exclude obstructive disease—7-38% of symptomatic patients with zero calcium score have obstructive CAD. 3
• In symptomatic patients with zero calcium score, 3.5% still had ≥50% arterial stenosis and 1.4% had ≥70% stenosis. 3

Age Restrictions

• Do not perform CT scanning in men <40 years old and women <50 years old due to very low prevalence of detectable calcium. 2, 3

High-Risk Patients

• Persons with >20% 10-year risk should not undergo CAC measurement, as they already warrant aggressive preventive therapy regardless of calcium score. 2

Clinical Algorithm for Decision-Making

Step 1: Calculate 10-year ASCVD risk using Pooled Cohort Equations 2

Step 2: Apply age criteria

• Patient must be 40-75 years old 1
• For women, preferably ≥50 years 2

Step 3: Determine risk category and appropriateness:

• <5% risk: Do not order CAC 2, 4
• 5-7.5% risk: Order CAC only if risk-enhancing factors present 1
• 7.5-20% risk: Order CAC when treatment decision uncertain 2, 1
• >20% risk: Do not order CAC; treat aggressively 2

Step 4: Confirm patient is asymptomatic

• No chest pain or anginal equivalents 3
• No known CAD 3

How CAC Results Guide Management

CAC Score = 0 (Very Low Risk)

• Indicates excellent prognosis with <1% annual risk for cardiac death or MI. 3
• Statin therapy can be withheld in most cases, with 10-year event rate of only 1.5-3.0%. 1
• Consider repeat CAC in 3-5 years to assess for progression. 3

CAC Score 1-99 (Mild Elevation)

• Favors statin therapy, especially for patients aged >55 years. 1
• Represents modest risk reclassification upward. 1

CAC Score ≥100 or ≥75th Percentile (High Risk)

• Initiate moderate-to-high intensity statin therapy. 1
• Event rate ≥20 per 1000 person-years. 1
• Intermediate-risk patients with CAC ≥300 had 2.8% annual rate of cardiac death or MI (equivalent to 28% 10-year rate). 2

CAC Score ≥300-400 (Very High Risk)

• High-intensity statin therapy is strongly recommended. 1
• Consider stress testing or advanced imaging to assess for myocardial ischemia. 3

Common Pitfalls to Avoid

• Ordering CAC in truly low-risk patients (<5% 10-year risk) without risk-enhancing factors wastes resources and exposes patients to unnecessary radiation (1.5 mSv). 3, 4
• Ignoring CAC >0 in "low-risk" patients underestimates atherosclerosis burden, as CAC represents only ~20% of total atherosclerotic burden. 1
• Repeating CAC too soon (less than 3-5 years) has limited utility in patients already on optimal medical therapy. 1
• Using CAC as a surrogate for detecting obstructive CAD in symptomatic patients is inappropriate due to poor specificity. 3
• Insurance may deny claims for inappropriate indications, leaving patients responsible for payment. 3
• Medicare does not routinely cover CAC scoring for screening purposes. 3

Technical Considerations

• Order as "CT Coronary Artery Calcium Score" or "Cardiac CT for Calcium Scoring" using ECG-gated multidetector computed tomography without contrast. 3
• Radiation exposure is relatively low (0.37-1.5 mSv), equivalent to 1-2 mammograms per breast. 2, 3
• Cost is typically <$100 at many imaging centers. 3
• Agatston score is the most widely used scoring system, defining calcific lesions as having CT density >130 Hounsfield units and area >1 mm². 3