Cholesterol, a fatty substance found in the body, can only travel through the bloodstream when it combines with specialized proteins known as lipoproteins. Because each type of lipoprotein differs in structure and function, some types of cholesterol, such as LDL, increase the risk of heart disease while others like HDL help protect against heart disease. Doctors utilize both absolute cholesterol levels and ratios to assess the risk for heart disease.
HDL Cholesterol
HDL cholesterol describes the cholesterol bound to high-density lipoprotein. This type of cholesterol contains very little fat, including both cholesterol and triglyceride, but high amounts of protein, making it denser than the other lipoproteins that carry cholesterol, like low-density lipoprotein, or LDL. Its unique structure allows it to pick up cholesterol and carry it to the liver for disposal from the body, making it known as the "good cholesterol." In determining the risk for heart disease, the higher the HDL levels the better.
Cholesterol Testing
The National Cholesterol Education Program developed by the National Heart Lung and Blood Institute recommends all adults age 20 or older test their cholesterol levels every five years. Doing this helps you to monitor your levels and assess your risk for heart disease. A lipid profile ordered as part of a routine physical examination requires no fasting and provides results for the amount of HDL and the total cholesterol -- the level of HDL, LDL and other small amounts of lipids like triglycerides -- together. Utilizing these results doctors can calculate your cholesterol ratio.
Cholesterol Ratio
Although the LDL cholesterol level is the most important in determining your risk for heart disease, it requires fasting, refraining from eating food, for at least 12 hours. Since this is not always possible, knowing your HDL and total cholesterol can estimate the level of LDL. Doctors determine the cholesterol ratio by dividing the total cholesterol by the HDL cholesterol. For example, a total cholesterol of 240 mg/dL and an HDL cholesterol of 40 mg/dL produces a cholesterol ratio of 6-to-1.
Heart Disease Risks
When doctors urge you to keep your cholesterol levels low, they are referring to your total cholesterol and your LDL cholesterol. On the contrary, you want your HDL levels to remain as high as possible, with levels over 60 mg/dL providing protection against heart disease. With high HDL levels and low total cholesterol levels, the cholesterol ratio remains low. The American Heart Association recommends maintaining a cholesterol ratio of 3.5 to 1 or lower. Those with a higher ratio should undergo further testing to determine their absolute LDL cholesterol level in order to develop the most effective course of treatment.
References
- MayoClinic.com: Cholesterol Ratio -- Is it Important; January 2010
- American Heart Association: Cholesterol Ratio
- National Heart Lung and Blood Institute: How is High Blood Cholesterol Diganosed?; September 2008
- National Heart Lung and Blood Institute: National Cholesterol Education Program
- American Heart Association: About Cholesterol; January 2011
