What are the indications for a computed tomography (CT) calcium score?

Indications for CT Calcium Scoring

CT calcium scoring is most strongly indicated for asymptomatic adults aged 40-75 years at intermediate cardiovascular risk (7.5-20% 10-year ASCVD risk) when treatment decisions about statin therapy remain uncertain. 1

Primary Indications

Intermediate Risk Patients (Class IIa Recommendation)

• Patients with 10-20% 10-year ASCVD risk should be considered for CAC scoring to guide statin therapy decisions, as this represents the strongest evidence-based indication with a Class IIa recommendation from the ACC/AHA. 2, 1
• CAC measurement is reasonable for cardiovascular risk assessment in this population, where test results can meaningfully reclassify risk and alter management. 2
• Intermediate-risk patients with CAC scores >300 have annual cardiac event rates of 2.8% (equivalent to 28% over 10 years), reclassifying them as high-risk. 2

Borderline to Low-Intermediate Risk (Class IIb Recommendation)

• CAC scoring may be reasonable for patients with 5-7.5% 10-year ASCVD risk (borderline) or 6-10% 10-year risk when risk-enhancing factors are present. 2, 1
• Risk-enhancing factors that support testing include: family history of premature CHD, persistently elevated LDL-C, metabolic syndrome, chronic kidney disease, or inflammatory diseases. 1

Low Risk with Family History

• Low-risk patients (<5% 10-year ASCVD risk) with a family history of premature coronary heart disease represent an appropriate indication for CAC scoring. 1, 3
• In this population, CAC >100 was associated with 10.4 times higher risk of CHD-specific mortality compared to CAC = 0, with a number needed to screen of only 9 to detect CAC >100. 3

Specific Clinical Scenarios

Risk Reclassification Tool

• CAC scoring provides superior risk prediction when combined with traditional ASCVD risk scores, improving risk classification by 12.2% even after 20 years of follow-up. 4
• In the highest ASCVD risk category, cardiovascular events occurred in only 14% with CAC = 0 versus 34.2% with CAC ≥400 over 20 years. 4
• In the lowest ASCVD risk category, events occurred in 2.4% with CAC = 0 versus 23.5% with CAC ≥400. 4

Shared Decision-Making

• CAC scoring is particularly valuable when patient and clinician are uncertain about initiating preventive therapy, as it provides objective data to guide discussions. 1
• The "power of zero" is clinically significant: patients with CAC = 0 have an annual event rate of only 0.027%, with 99.9% negative predictive value for cardiovascular events. 5

Incidental Detection

• The Society of Cardiovascular Computed Tomography and Society of Thoracic Radiology recommend reporting CAC on all non-gated chest CT scans regardless of indication or patient risk status. 2
• Reporting CAC on non-gated chest CTs altered statin recommendations in 63% of patients, including 85% of intermediate-risk patients. 6

Contraindications and Inappropriate Uses

Not Recommended Populations

• Men <40 years and women <50 years should not undergo CAC scoring due to low prevalence of detectable calcium and radiation exposure concerns. 2, 1, 7
• Low-risk patients (<6% 10-year risk) without family history of premature CHD should not undergo CAC measurement. 2, 1
• High-risk patients (>20% 10-year risk) generally do not need CAC scoring as they already warrant aggressive preventive therapy. 2

Inappropriate Testing

• Repeat coronary calcium testing is considered inappropriate and should not be performed. 1
• Serial imaging for assessment of progression of coronary calcification is not indicated. 2
• Screening asymptomatic patients using coronary CT angiography (rather than calcium scoring) is inappropriate. 1

Clinical Action Based on Results

CAC Score = 0

• Statin therapy can be withheld and risk reassessed in 5-10 years, unless higher-risk conditions are present. 1
• This applies even to intermediate-risk patients, as the negative predictive value is 99.9%. 5

CAC Score 1-99

• Initiate statin therapy for patients ≥55 years of age. 1
• Consider patient preferences and risk-enhancing factors for younger patients. 1

CAC Score ≥100 or ≥75th Percentile

• Initiate statin therapy regardless of age. 1
• Consider functional stress testing, as approximately 48.5% of patients with CAC >400 have abnormal perfusion. 8

CAC Score >300-400

• Initiate high-intensity statin therapy and consider screening for clinically silent ischemia. 7, 8
• Patients with CAC >400 have 10.8-fold increased risk of CHD death or MI over 3-5 years compared to CAC = 0. 2

Important Caveats

• CAC = 0 does NOT exclude non-calcified plaque or obstructive coronary disease; 7-38% of symptomatic patients with CAC = 0 have obstructive disease. 1
• CAC scoring reflects atherosclerotic burden but does not directly assess degree of stenosis or plaque vulnerability. 7, 8
• Radiation dose is relatively low (0.9-1.5 mSv), comparable to 1-2 mammograms, when prospective ECG-gating is used. 2, 1, 7
• The test should be performed using prospectively ECG-triggered scanning with 2.5-3.0 mm slice thickness to minimize radiation exposure. 2, 7