Cholesterol ratio is the ratio of HDL ("good") cholesterol to LDL ("bad") cholesterol. When too much LDL cholesterol circulates in the blood, it can slowly build up in the walls of the arteries that feed the heart and brain and cause atherosclerosis.

About a third of blood cholesterol is carried by high-density lipoprotein (HDL). HDL cholesterol is known as the "good" cholesterol because a high level of it seems to protect against heart attack.