Cholesterol, total. Cholesterol is a form of fat (lipid) bound to protein known as a lipoprotein, and is an essential component of all cell membranes (boundaries) - but an excess of it during a health screening is linked to an increased risk of heart and blood vessel disease. The total figure is useful, but it is more helpful to know the levels of the two parts which make up the bulk of the cholesterol molecule - HDL and LDL.