Blood tests are needed to determine how much of your cholesterol is carried by high-density lipoproteins (good) and low-density lipoproteins (bad).

Publications International, Ltd.

Doctors test cholesterol levels to determine how much cholesterol is carried by low density cholesterol and how much is carried by HDL cholesterol. Determining these cholesterol levels can indicate whether more cholesterol is remaining in the bloodstream, which can lead to atherosclerosis, a condition in which plaque builds up in the arteries.

Blood helps to transport cholesterol through the body. Because cholesterol is a lipid, it doesn't mix with water. Blood, however, is made up of a substantial amount of water. Therefore, in order to move cholesterol through the bloodstream, the body wraps it in proteins, forming lipoproteins. The lipoproteins glide through the bloodstream like microscopic submarines carrying cargoes of cholesterol to destinations in the body.

Two types of lipoproteins that play a major role in transporting cholesterol are low-density lipoproteins (LDLs) and high-density lipoproteins (HDLs). LDLs are called the "bad" cholesterol, and HDLs are called the "good" cholesterol.

Two other types of lipoproteins include very low-density lipoproteins (VLDLs) and chylomicrons. VLDLs carry triglycerides (fat molecules) that are made in the liver, along with some cholesterol, to cells where the triglycerides can be stored. Depositing the triglycerides in the cells leaves mostly cholesterol, turning the VLDLs into plain old LDLs. Chylomicrons are responsible for picking up dietary cholesterol from the intestines after it has been absorbed from food.

The level of cholesterol in your blood is expressed in "milligrams per deciliter (mg/dL)," which indicates the weight of the cholesterol found in one deciliter of blood. Blood-cholesterol tests usually measure the total amount of cholesterol in your blood. Tests and calculations can also be performed to see how much of that cholesterol is contained in the form of LDLs and HDLs.

If cholesterol is normally present in your blood, why should you worry about it? The reason is that the total amount of cholesterol in your blood reveals how efficiently your body is using and managing cholesterol. Excessive cholesterol in your blood may mean that something is going wrong with how your body is using cholesterol.

­When more of the cholesterol in your blood is being carried by HDLs, the "good" cholesterol, there is less danger of cholesterol accumulating in the body. If LDLs, the "bad" cholesterol, are carrying more of the cholesterol, the balance is tipped in favor of cholesterol remaining in the body.

­­We'll start out by learning about the "bad" form of cholesterol. The next page explains LDL cholesterol.