Abstract: This invention relates to a labelled diagnostic composition for testing presence of or propensity for atherosclerosis and coronary artery disease and the like comprising components which mimic essential features of an exogenous lipoprotein transport particle, said composition being capable of metabolisation by normal physiological pathways such that at least one labelled metabolite is detectable in the blood or bodily waste of a patient being tested. Furthermore, it also relates to a method of determining the presence of or propensity for atherosclerosis or coronary artery disease and the like in a patient requiring such determination comprising administering to said patient a labelled diagnostic composition which mimics essential features of an exogenous lipoprotein transport particle, and measuring the quantity of labelled metabolite in the bodily waste or blood of said patient so as to determine the quantity of labelled diagnostic composition successfully metabolised by said patient.