blood low density lipoprotein cholesterol level Measurement of the amount of cholesterol, a eukaryotic sterol that in higher animals is the precursor of bile acids and steroid hormones and a key constituent of cell membranes, carried in low-density lipoprotein (LDL) molecules in a specified volume of blood, the fluid that circulates through the heart, arteries, capillaries and veins carrying nutrients and oxygen to the body tissues and metabolites away from them. LDL constitute a class of relatively large, heterogeneous lipoprotein particles, complex molecules that consist of a protein membrane surrounding a core of lipids. The LDL class of lipoproteins has a density between 1.019 and 1.063 g/ml. In some animal species, such as canine and rodents, this may overlap with the HDL1 class and be designated LDL/HDL1. Values for density ranges of the lipoprotein classes are approximate. The classes may be defined differently by different researchers, in part because class definitions depend on the number of subclasses into which the lipoprotein fractions are divided. blood LDL level blood LDL-C level blood lipoprotein cholesterol level