serum sterol level blood cholesterol level serum cholesterol level 2014-03-24T13:36:35Z JSmith Not4Curation 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, in a specified sample of serum, the clear liquid that separates from blood after it has clotted completely, i.e. blood plasma from which fibrinogen has been removed. Cholesterol in the serum is associated with various lipoproteins.