The lipid or fat content of the blood is known to be correlated with the risk of developing cardiovascular disease.  The main lipid of concern is cholesterol, which can be found in the blood in several different forms.  This is because cholesterol does not dissolve in the water of which blood is composed.  In order for it to be transported through the blood stream the body attaches cholesterol molecules to protein and constructs a tiny particle. The combination of cholesterol and protein is called a lipoprotein (literally a lipid protein).  These tiny particles come in various densities: some are very dense and will eventually sink to the bottom of a tube of blood, others are lighter and will float to the top of a tube of blood (very much like cream floats to the surface of milk). Thus, we have high, low, and very-low density lipoproteins and each of these has a different influence on the body.  When we measure the “Total Cholesterol” in the blood we are actually measuring the combination of high, low, and very-low density lipoprotein. Because each of these fractions means something different, it is important to know what the amount of each.

The LDL-Cholesterol (Low Density Lipoprotein Cholesterol) (LDL-C) constitutes the largest fraction of cholesterol in the blood.  This is the “bad” cholesterol and the higher its value, the greater is the risk of developing heart disease. This is the cholesterol that travels from the liver (where the lipoprotein is assembled) to the tissues where it has an important metabolic role.  However, along the way, it can become trapped in the walls of blood vessels where it causes a tiny lesion (called a plaque) and contributes to the process of narrowing the blood vessels, like rust in a water pipe.

The HDL-Cholesterol (High Density Lipoprotein Cholesterol) (HDL-C) is a smaller fraction and represents the “good” cholesterol.  This is the cholesterol that travels out of tissues.  Opposite to LDL-C, the higher the value of HDL-C the lower the risk of cardiovascular disease.

The VLDL-Cholesterol (Very Low Density Lipoprotein Cholesterol) (VLDL-C) is cholesterol that is wrapped up with the triglyceride fats in the blood stream.  Triglycerides (TG) are oils consisting of three fatty acid chains attached to a glycerol molecule.  Triglycerides are greatly elevated in diabetes when out of control, in liver disease, and in certain inherited disorders.  Triglycerides rise after meals, which is why a fasting period is required before measuring lipids. Cholesterol found in VLDL is neutral in terms of atherosclerosis and is another reason why the measurement of Total Cholesterol may be misleading.

How do you interpret the results?

There are various ways to interpret the results of these tests. You may read about cholesterol in magazine or newspaper articles and be confused by the fact that the values are so much different from what you have obtained in the lab.  This is because much of the material you read is from the USA and is expressed in conventional units rather than the SI units that most of the world employs.   To convert American units (mg/dL) into Canadian units (mmol/L) you must multiply the American value by 0.026 .

The following links describe the interpretation of lipid results based on the most recent (2006) Canadian clinical guidelines.

 Canadian Journal of Cardiology 2006 guidelines

Ontario Association of Medical Laboratories