Fractionated Lipid Testing

Fractionated Lipid Testing

The cholesterol test is a quantitative analysis of the cholesterol levels in a sample of the patient's blood. In the United States, is estimated that more than 200 million cholesterol tests are performed each year. Generally, the measurement taken is known as Total serum cholesterol (TC) is. However, to better asses the risk for atherosclerosis (coronary artery disease, or CAD) doctors sometimes order a complete lipoprotein profile. Cholesterol is a fatty substance and cannot be dissolved in water. It must combine with a protein molecule called a lipoprotein in order to be transported in the blood. The full lipoprotein profile consists of measuring the triglyceride levels and lipoproteins density.


Triglyceride is a chemical compound that forms 95% of the fats and oils stored in animal or vegetable cells.

Lipoproteins present in the human body differ in the amount of cholesterol that they carry in comparison to other fats and fatty acids, and in their functions in the body. These are the main types of lipoproteins classified according to its density:

Chylomicrons. These are normally found in the blood only after a person has eaten foods containing fats. They contain about 7% cholesterol. Chylomicrons transport fats and cholesterol from the intestine into the liver, then into the bloodstream. They are metabolized in the process of carrying food energy to muscle and fat cells
Very low-density lipoproteins (VLDL). These lipoproteins carry mostly triglycerides, but they also contain 16-22% cholesterol. VLDLs are made in the liver and eventually become IDL particles after they have lost their triglyceride content.
Intermediate-density lipoproteins (IDL). IDLs are short-lived lipoproteins containing about 30% cholesterol that are converted in the liver to low-density lipoproteins (LDLs).
Low-density lipoproteins (LDL). LDL molecules carry cholesterol from the liver to other body tissues. They contain about 50% cholesterol. Extra LDLs are absorbed by the liver and their cholesterol is excreted into the bile. LDL particles are involved in the formation of plaques (abnormal deposits of cholesterol) in the walls of the coronary arteries. LDL is known as "bad cholesterol."
High-density lipoproteins (HDL). HDL molecules are made in the intestines and the liver. HDLs are about 50% protein and 19% cholesterol. They help to remove cholesterol from artery walls. Lifestyle changes, including exercising, keeping weight within recommended limits, and giving up smoking can increase the body's levels of HDL cholesterol. HDL is known as "good cholesterol."

With the identification of levels for multiple subclasses of lipid abnormalities, lipid-lowering therapies can be prescribed more accurately, particularly in high-risk patients such as those with type 2 diabetes. Now, it’s important to understand that two patients with the same total cholesterol level can have very different lipid profiles and different risk for CAD as consequence of the difference in density and cholesterol content of lipoproteins.


When assessing the patient's degree of risk, doctors often use the ratio of the total cholesterol level to HDL cholesterol. A low TC/HDL ratio is related with a lower degree of risk. Then, the type of cholesterol in the blood is as important as the total quantity, and the critical factor is the level of HDL cholesterol in the blood serum.


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