Risk assessment is regarded as the first step in the clinical management of patients with cardiovascular risk factors. Traditionally, the Framingham Risk Score, the PROCAM score in Germany and the SCORE (Systemic Coronary Risk Evaluation) in Europe are most commonly used and most widely available. These risk assessment algorithms are often used to project short term and intermediate term risk, but not lifetime risk. In addition, these projections are used to determine appropriate candidates for risk reduction therapy. Treatment intensity is often linked to severity of risk. However, a significant accumulation of data support the premise that calcium scoring may further refine risk and reclassify those in the intermediate risk category into either low risk or high risk categories. In other words, calcium scoring has incremental prognostic value [26–32]. Shaw et al. [26] demonstrated that coronary calcium scores of over 1,000 posed a 12 times relative risk for all cause mortality versus traditional Framingham risk factors which posed a two times relative risk. This finding held true for both diabetics and non-diabetics. These findings have been confirmed by a multitude of studies including Budoff et al. [30] who observed a 10 year survival rate of 99.4 % in patients with a calcium score of 0 versus an 88.7 % survival rate for those with a score of > 100. The MESA (Multi Ethnic Study of Atherosclerosis) [32] was one of the latest land mark studies demonstrating the incremental risk prediction of coronary calcium. This study was a prospective study of 6,722 patients in six cities in the United States. The MESA study demonstrated a 3.5–10 times incremental risk of hard cardiovascular events based on coronary calcium burden, where those with a calcium score of >300 had a 10-fold higher risk compared to a 3.5-fold higher risk for a score of ≤100. In fact, the most recent guidelines for stable ischemic heart disease indicate that a calcium score of 100 portends a relatively low cardiovascular risk while that of >400 represents high risk (Fig. 6.7) [33].

It has also been shown that coronary calcium scoring is able to more effectively and specifically classify patients into high or low risk groups than risk factor algorithms alone [32, 34–36]. Calcium scoring performs best when applied to the intermediate risk population and serves to reclassify these individuals into high or low risk strata. In other words, coronary calcium scoring places more patients in the most extreme risk categories than traditional risk factor based scoring systems alone. The yield of coronary calcium scoring in very low risk individuals is very low [37]. In addition, a subset of the MESA study proposes an arterial age calculator to assess the arterial age of a patient as related to their chronological age [38]. Furthermore, the degree of coronary calcification has also been shown to be predictive of the frequency and type of coronary revascularization [39]. The 2013 ACC/AHA Guideline on the Assessment of Cardiovascular Risk indicate that a calcium score of ≥300 or ≥75th percentile support revising a patients cardiovascular risk upward from their pre-calcium score risk category [40].

While the absence of coronary calcium portends a favorable risk prediction [41–44], it does not preclude the presence of a clinically significant atherosclerotic plaque. The absence of coronary calcification does not absolutely exclude obstructive coronary disease or the need for revascularization [45]. Gottlieb et al. [45] demonstrated that 19 % of patients without detectable coronary calcium who were referred for conventional angiography had >50 % coronary stenoses. It should be noted that these patients prompted enough clinical suspicion to be referred for invasive coronary angiography in the first place. Sarwar et al. [42] demonstrated a negative predictive value for obstructive coronary stenoses of 93–98 % when no coronary calcium was detected. But the negative predictive value for obstructive coronary artery disease was not zero. Thus, while in the asymptomatic patient with a zero calcium score no further treatment is necessary, in the symptomatic patient with high clinical suspicion, the absence of coronary calcification should not discourage the clinician from more aggressive testing to exclude obstructive coronary artery disease. It should also be noted that calcium scoring is less predictive in those less than 45 years of age.

Calcium scoring may be used to assess atherosclerotic disease progression over time. Progression of coronary calcification is often observed over periods of 3–7 years to a degree related to the extent and severity of the baseline coronary calcification [46, 47]. Progression of coronary calcification over time has been shown to portend a worse prognosis and predict future cardiac events [48–51]. The degree of baseline calcification and its progression have been associated with the greater prescription and adherence to aspirin and statin therapy and to better risk factor control without greater downstream medical testing [52–54]. However, serial coronary calcium scoring scans are not routinely recommended since improvement in outcomes based on such a practice has not yet been definitively established.