Coronary artery calcium score as a gatekeeper for further testing in patients with low probability of obstructive coronary artery disease: a cost-effectiveness analysis

Abstract

Abstract Funding Acknowledgements Type of funding sources: None. Introduction Current guidelines recommend not to routinely test patients with chest pain and low pretest probability (PTP <15%) of obstructive coronary artery disease (CAD) but envisage the use of risk modifiers such as coronary artery calcium score (CACS) to refine patient selection for testing. The aim of this study was to assess the cost-effectiveness (CE) of three different testing strategies in the approach to symptomatic patients with low PTP of obstructive CAD: A) not test; B) perform CACS, withholding testing if = 0 and proceeding to coronary CT angiography (CCTA) if > 0; and C) perform CCTA in all cases, without prior CACS. Methods We developed a CE model using data from a two-centre study of 1385 patients with non-acute chest pain and PTP <15% who underwent CACS immediately followed by CCTA. Key input data included the proportion of patients with obstructive CAD on CCTA (10.3%), the proportion with CACS=0 (57%), and the negative predictive value of CACS for obstructive CAD on CCTA (98.9%), which was considered the gold standard for this simulation. The CE of each strategy was defined as the cost per correct diagnosis. Direct costs were calculated using the price list from the Portuguese National Health Service. Indirect costs, including incidental findings, were estimated according to the literature. The cost attributable to a false-negative was set at 3 times the cost of a false-positive, as customary. Results Not testing would correctly classify 89.7% of cases, and would cost €121.433 per 1000 patients, due to the cost imputed to false negatives. Using CACS as a gatekeeper for CCTA would correctly diagnose 98.9% of cases, and cost €247.116 per 1000 patients. Employing CCTA as first-line test would correctly classify all patients, at a cost of €271.007 for 1000 diagnosed patients. Overall, the added cost for an additional correct diagnosis was €1.366 for CACS±CCTA strategy vs. no testing, and €2.172 for CCTA vs. CACS±CCTA. The corresponding cost-effectiveness thresholds (CET) were €943–€3.450 for men; and €1.527–€1.972 for women (Table 1). Conclusions Not testing patients with low PTP of obstructive CAD should be disfavoured unless the CET is below €1.366 per correct diagnosis. First-line CCTA yields the most correct diagnoses and is cost-effective above CET over €2.172 per additional correct diagnosis. Using CACS as a gatekeeper for further testing is cost-effective between these thresholds, which are wider for men than for women. These findings may inform decisions on testing, but the most suitable strategy will ultimately depend on the costs and amount of missed diagnoses stakeholders are willing to accept.