Which patients may benefit from coronary artery calcification scoring?
Although we still have no evidence from randomized trials that patients have better outcomes if we measure the calcification in their coronary arteries, a growing body of evidence shows that we can estimate risk more accurately than with a risk model score alone if we also score coronary artery calcification in asymptomatic patients, especially those at intermediate risk.
Current guidelines1 recommend using the Framingham Risk Score or a similar tool to estimate coronary risk in asymptomatic patients, but these tools have only modest accuracy. Calcification scoring is accurate, inexpensive, quick, widely available, low-risk, and does not appear to increase medical costs afterward. In addition to improving risk stratification, it may also encourage patients to adhere better to drug therapy and lifestyle modification.
HOW IS CORONARY ARTERY CALCIFICATION MEASURED?
Calcification of the coronary arteries is synonymous with atherosclerosis. It can easily be detected with computed tomography without contrast (Figure 1), and the amount can be quantified with a scoring system such as the volumetric score or the Agatston score. The latter, which is more commonly used, is based on the product of the area of the calcium deposits and the x-ray attenuation in Hounsfield units.
Scores can be roughly categorized (with some overlap owing to data from different studies) as:
- Low risk: 0 Agatston units (AU)
- Average risk: 1–112 AU
- Moderate risk: 100–400 AU
- High risk: 400–999 AU
- Very high risk: 1,000 AU.2
The actual test takes only a few seconds, and the patient can usually be out the door in 15 minutes or less. It does not require iodinated contrast and the radiation dose is minimal, usually less than 1 mSv, equivalent to fewer than 10 chest radiographs.3
The cost is typically between $200 and $500. The test is usually not covered by health insurance, but this differs by insurer and by state; for example, coverage is mandated in Texas, and the test is covered by United Healthcare.
WHAT IS THE EVIDENCE IN FAVOR OF CALCIFICATION SCORING?
Cohort studies with long-term follow-up show that calcification scoring has robust prognostic ability. A pooled analysis of several of these studies2 showed that a higher score strongly correlated with a higher risk of cardiac events over 3 to 5 years. Compared with the risk in people with a score of 0, the risk was twice as high in those with a score of 1 to 112, four times as high with a score of 100 to 400, seven times as high with a score of 400 to 499, and 10 times as high with a score greater than 1,000.2
A cohort study of more than 25,000 patients had similar conclusions about the magnitude of risk associated with coronary calcification.4 It also found that the 10-year risk of death was 0.6% in patients with a score of 0, 3.4% with a score of 101 to 399, 5.3% with a score of 400 to 699, 6.1% with a score of 700 to 999, and 12.2% with a score greater than 1,000.
Although progression of coronary artery calcification may predict the risk of death from any cause,5 the clinical utility of serial measurements is not yet apparent, especially since statin therapy—our front-line treatment for coronary disease—has not been shown to slow the progression of calcification.
