Cholesterol is a lipid molecule supplied via the diet and through hepatic cholesterol production. Therefore, liver failure, malnutrition, and diseases reducing intestinal absorption are the main causes of abnormally low cholesterol. Elevated cholesterol, on the other hand, can be caused by obesity or eating before blood sampling, or by diseases affecting lipid homeostases, such as diabetes mellitus, hypothyroidism or Cushings’s disease, nephrotic syndrome, and biliary obstruction or mucocele. 

Circulatory cholesterol is carried in lipoprotein particles either in its esterified form within lipoprotein particles or its free form on the outer surface of lipoprotein particles. The two major lipoprotein particles for cholesterol transport are HDL and LDL, of which HDL is responsible for transporting cholesterol away from tissues, and LDL into tissues. While VLDL particles are mainly used to transport triglycerides to tissues, cholesterol is also a constituent of VLDL particles. The lower atherosclerosis risk in dogs than humans is caused by the fact, that in canine hyperlipidemic states, cholesterol is transferred into HDL particles, creating very large, cholesterol-rich HDL particles. These are less atherogenic than the LDL particles, in which cholesterol accumulates in human hypercholesterolemia.