Calcium scoring improves clinical management in patients with low clinical likelihood of coronary artery disease

Background: Coronary artery calcium scoring (CACS) improves management of chest pain patients. It is however unknown whether the benefit of CACS is dependent on the clinical likelihood (CL).
Objective: To investigate in which patients CACS has the greatest benefit when added to a CL model.
Methods: Based on data from a clinical database, the CL of obstructive coronary artery disease (CAD) was calculated for 39,837 patients referred for cardiac imaging due to symptoms suggestive of obstructive CAD. Patients were categorized according to the risk factor-weighted (RF-CL) model (very low, ≤5%; low, >5-≤15%; moderate >15-≤50%; high, >50%). CL was then re-calculated incorporating the CACS result (CACS-CL). Re-classification rates and the number needed to test with CACS to re-classify patients were calculated and validated in three independent cohorts (n=9,635).
Results: In total, 15,358 (39%) patients were down- or up-classified after including CACS. Re-classification rates were 8%, 75%, 53%, and 30% in the very low, low, moderate, and high RF-CL categories, respectively. Re-classification to very low CACS-CL occurred in 48% of re-classified patients.
The number needed to test to re-classify one patient from low RF-CL to very low CACS-CL was 2.1 with consistency across age, sex, and cohorts. CACS-CL correlated better to obstructive CAD prevalence than RF-CL.
Conclusion: Added to a RF-CL model for obstructive CAD, CACS identifies more patients unlikely to benefit from further testing. The number needed to test with CACS to re-classify patients depends on the pre-test RF-CL and is lowest in patients with low (>5-≤15%) likelihood of CAD.