To validate the use of Corus CAD (Age/Sex/Gene Expression score - ASGES) blood assay in subjects who are referred for the work-up of coronary artery disease. The study will evaluate the clinical utility of a gene expression test Corus CAD (Age, Sex, Gene Expression Score - ASGES) in subjects referred for myocardial perfusion imaging (MPI) work-up for suspected obstructive atherosclerotic coronary artery disease (CAD). The Corus CAD is a gene expression test that quantify the expression of multiple genes from circulating peripheral blood cells to detect the presence of clinically significant obstructive CAD in patients with chest pain.