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What is a cholesterol test?

Anthony L. Komaroff, MD
Internal Medicine
Although total cholesterol levels are important, it's even more important to look at levels of different types of cholesterol, particularly low-density lipoprotein (LDL) and high-density lipoprotein (HDL). That is why the National Cholesterol Education Program (NCEP) recommends that everyone age 20 or older undergo a fasting lipid profile test (also called a full lipid profile or lipoprotein analysis) every five years. This test measures not only total cholesterol, but also LDL, HDL, and triglyceride levels.
Cholesterol is a soft, waxy substance that carries digested fat from your liver to other parts of your body. Cholesterol and other fats travel together in your blood in packages called lipoproteins. Different types of lipoproteins play different roles in the health of your heart:
  • Low-density lipoprotein (LDL) cholesterol or "bad cholesterol" can build up and help form a substance called plaque in your arteries. Plaque can cause serious risks for your heart and other organs.
  • High-density lipoprotein (HDL) cholesterol or "good cholesterol" can prevent or slow the buildup of plaque.
  • Triglycerides are the most common type of fat in your blood. Studies show that many people with heart disease have high triglycerides.
Merle Myerson, MD
Cardiology (Cardiovascular Disease)
Checking cholesterol, or more accurately lipid levels, is fairly simple--all it takes is a blood test.  Many people ask if the blood test needs to be fasting and the answer I share with my patients is yes.  I will explain why in just a minute.

First, what are the numbers you will get on a standard lipid panel?  They are: total cholesterol, LDL-cholesterol, HDL-cholesterol and triglycerides.  The "total cholesterol" is the measure of all the cholsterol in your blood.  This includes the HDL cholesterol, known as the "good."  Because of this, the number for your total cholesterol does not accurately reflect how much bad cholesterol you have.  It can be high if your good cholesterol is high.  It is therefore important to look at the other numbers as well.

The HDL-cholesterol is the good cholesterol because it carries the bad cholesterol from your body and back to the liver for removal.  Triglycerides are another type of lipid, or fat, that is associated with risk for cardiovascular disease.  At very high levels it can be a cause for pancreatitis, an inflammation of the pancreas which can be very serious.  The LDL-cholesterol number that you see on your lab report is most often a "calculated" number, meaning that the value is determined by using a formula.  This formula is accurate unless the triglycerides are over 400 mg/dL.  In terms of fasting, the total, HDL, and LDL are minimally affected by eating, however the triglycerides can change signficantly if you have eaten.  It is best to have your blood test after a 12-hour fast. 

What I talk about above is the most common blood test but national guidelines have recommended additional measures.  Why is this?  The LDL-cholesterol measure does not completely account for all the bad cholesterol in your blood.  The "non-HDL cholesterol" better reflects the total amount of cholesterol that puts you at risk for cardiovascular disease.  It is calculated based on the measure of total and HDL cholesterol (non-HDL-cholesterol = total cholesterol - HDL-cholesterol). Another way to determine how much bad cholesterol you have is by measuring "apolipoprotein B."  This is a component of LDL-cholesterol and other lipid particles that cause atherosclerosis. 
 
A blood cholesterol test gives your physician important information about your risk for cardiovascular disease and can also be used to see if medications prescribed to lower cholesterol levels are working. This blood test is used to measure total cholesterol levels, LDL (or “bad”) cholesterol, HDL (or “good”) cholesterol and triglycerides. When all types of blood fat are checked at the same time, it is called a lipoprotein profile.

LDL (low-density lipoprotein) cholesterol is often referred to as “bad” cholesterol because it causes plaque to build up inside the arteries. The maximum LDL for health in patients varies with medical history. An LDL cholesterol reading of over 130 mg/dl places someone at higher risk for cardiovascular events. With existing disease, the maximum may be 100 mg/dl, or even lower -- for example, 70 mg/dl if you have had a heart attack.

HDL (high-density lipoprotein) cholesterol is called “good” cholesterol because it helps keep cholesterol from building up inside the blood vessels. An HDL cholesterol reading below 40 indicates an increased risk for cardiovascular disease, and higher is always better.

Triglycerides are the third type of blood fat measured by the test. A triglyceride level of 200 or more indicates an increased risk of cardiovascular disease.

Generally you will be asked to avoid eating or drinking for 8-12 hours before having blood drawn for cholesterol screening (fasting lipid profile). However, in some instances, general screening can be done without fasting.

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Important: This content reflects information from various individuals and organizations and may offer alternative or opposing points of view. It should not be used for medical advice, diagnosis or treatment. As always, you should consult with your healthcare provider about your specific health needs.