Cholesterol does not travel freely in the bloodstream. Rather, cholesterol is carried through the blood by particles called lipoproteins. Cholesterol also behaves differently depending on which type of lipoprotein carries it. Low-density lipoproteins (LDL) deposit excess cholesterol on the artery linings (LDL cholesterol is the “bad” cholesterol), and high-density lipoproteins (HDL) remove excess cholesterol from the blood (HDL cholesterol is the “good” cholesterol).

Triglycerides are another type of substance closely related to cholesterol. They are mostly carried throughout the bloodstream by particles called chylomicrons or very low-density lipoproteins (VLDLs). While less is known about triglycerides, in general, there is some evidence to suggest that they are a particularly important cause of coronary artery disease among women and people with other risk factors such as Diabetes and obesity.

According to the new guidelines released in May 2001 by the NHLBI’s National Cholesterol Education Program (NCEP), everyone age 20 and older should have their cholesterol and triglyceride levels measured at least once every five years.

This blood test is done after a nine- to 12-hour fast and provides information about your total cholesterol (TC), LDL and HDL cholesterol, and triglycerides. If your total blood cholesterol is 200 milligrams (mg) per deciliter (dL) or more, or if your HDL level is less than 40 mg/dL, you should talk to your doctor about ways to lower your cholesterol, which may include changing your diet, increasing exercise, or medication. 

HDL cholesterol protects against heart disease. This means that higher numbers of HDL cholesterol are better. A level less than 40 mg/dL is considered low and a major risk factor for the development of coronary artery disease. HDL levels of 60 mg/dL or more help to lower your risk for heart disease.

Triglycerides also can raise heart disease risk. Levels that are borderline high (150-199 mg/dL) or high (200 mg/dL or more) may require treatment for some people.

The NHLBI classification of the optimal level of LDL cholesterol is less than 100 mg/dL. Borderline high is 130-159 mg/dL, and very high is 190 mg/dL and above. High LDL cholesterol always requires attention. Your chance of developing coronary artery disease increases if you also have one or more other heart disease risk factors, such as high blood pressure, diabetes, and/or an early family history of heart disease.

The following table shows the NHLBI’s classification of all cholesterol levels.