How Cholesterol Is Measured
Cholesterol is measured in milligrams per deciliter of blood (mg/dL). Several different types of blood cholesterol can be measured, and high levels of some types are worse or better than high levels of other types. Types of cholesterol include the following:
- Total blood cholesterol
- HDL (high-density lipoprotein) cholesterol ("good" cholesterol)
- LDL (low-density lipoprotein) cholesterol ("bad" cholesterol)
- Triglycerides ("backbone" of many types of fat)
Total blood cholesterol is the most common cholesterol measurement. It measures the concentration of fat (lipid) in the bloodstream, including cholesterol and triglyceride molecules contained in LDL, HDL, and other lipid particles.
Total blood cholesterol levels can be used to help determine if LDL and triglyceride levels are likely to be normal or elevated. If total cholesterol levels are elevated, a lipid profile is used to determine which lipid level is too high.
HDL ("good") cholesterol may help protect against atherosclerosis by preventing cholesterol from depositing on arterial walls as it circulates in the bloodstream. Low HDL levels may be caused by a genetic predisposition, lack of exercise, smoking and/or obesity.
Some physicians believe it is important to assess the ratio between total blood cholesterol and HDL cholesterol. The ratio is calculated by dividing the HDL number into the total cholesterol number. For example, total cholesterol of 200 mg/dL and an HDL of 40 mg/dL would yield a ratio of 5:1 (200/40). A ratio below 5:1 is desirable and the optimum ratio is about 3.5:1.