Understanding Cholesterol: The Role of Triglycerides & the 5-Factor Calculation

When it comes to cholesterol, we all want to "know our numbers." Knowing how triglycerides figure into this equation will help us take charge of our cardiovascular health.

Cholesterol vs. Triglycerides

• There are two types of blood lipids, cholesterol and triglycerides. Cholesterol levels are generally more stable. Triglyceride levels, however, respond quickly to dietary carbohydrate and fat.

Blood Lipids

• Cholesterol and triglycerides in blood are bound to lipoproteins, which contain fat. Cholesterol is bound to HDL(high-density lipoproteins), LDL (low-density lipoproteins) and VLDL(very low density lipoproteins). Triglycerides are carried after a meal by chylomicrons, and longer term by VLDL. So VLDL is the only protein that carries both cholesterol and triglycerides.

Direct Measurement

• Labs measure total cholesterol (TC), HDL and total triglycerides(TG) directly. The tests for LDL and VLDL are more difficult, so instead these figures are calculated indirectly.

Indirect Calculation

• In 1972, William Friedewald, a medical doctor, developed what is now known as the Friedewald equation to make these calculations: TC (known) = LDL + HDL (known) + VLDL (which is TG/5). As of 2008, Friedewald was clinical professor of public health and medicine at Columbia University.

Why Divided by Five

• The triglyceride figure is divided by five because, with average triglyceride levels, one-fifth of the total is the amount of cholesterol bound with triglycerides in VLDL.

Limits of Reliability

• If the triglyceride level is above 400, the VLDL calculation is not considered accurate. This is one reason why patients are asked to fast prior to a cholesterol blood test. Fasting gives time for chylomicrons to clear the blood, leaving most triglycerides in VLDL form.