Calcium scoring: criteria for evaluating its effectiveness.

Abstract

Engineering advances in CT have produced multi-slice instruments that can scan large areas of the body in short periods of time, and such instruments now permit high resolution examination of entire anatomic regions (eg, the chest) in a single breath hold. Alternatively, these instruments can quickly scan small areas (such as the heart) with very high resolution in a very short period of time (eg, diastole). Using such CT scanners, there is no question that coronary artery calcium can be detected in small quantities and scored accurately. However, coronary calcium screening, like all screening procedures, poses a significant dilemma: early detection in a few is almost always accompanied by negative consequences for others (eg, false positives causing anxiety and unnecessary work-up, and false negatives causing delayed treatment and false reassurance). How do we balance the benefits to a few against the negative effects to others? That is the subject of this paper. A starting point for resolving the screening dilemma is to count the number of patients needed to be screened to benefit one patient (the NNS), and conversely, to determine the number of patients screened before harming one patient (NSH). Another approach is to apply published criteria suggested for the evaluation of a screening program targeted at early disease detection. In this review article, we propose 10 criteria for evaluating the effectiveness of a screening test designed to detect a risk factor for disease (ie, calcium scoring as a risk factor for coronary artery disease). We discuss how these criteria can be used to estimate NNS and NSH. Although this work focuses on coronary calcification screening, reference is made as well to other areas, such as lung and colon cancer screening.