Alternate Names : Low-Density Lipoprotein
An LDL test measures the level of low-density lipoprotein, or LDL, in the blood. LDL is also called the bad carrier for cholesterol. Cholesterol is a waxy substance that is used for many body processes. The LDL test is usually done as part of a lipid profile test that also includes total cholesterol, HDL test, and triglycerides.
Who is a candidate for the test?
An LDL test may be used to evaluate a person's risk for various conditions. Adults over the age of 20 should be tested every five years for cholesterol, LDL, HDL, and triglycerides. High LDL levels increase a person's risk for the following:
arteriosclerosis, or narrowing of the arteries
coronary heart disease, which is also called CHD
early death from heart disease
LDL results are evaluated differently in people with certain risk factors. People with CHD and CHD risk equivalents have the strictest LDL goals. If a person has CHD risk equivalents, it means that he or she has the same level of risk for a major heart related problem as someone who already has heart disease. These conditions include:
multiple risk factors that give the person a greater than 20% chance of developing CHD within 10 years
other clinical signs of atherosclerosis, such as peripheral arterial disease, abdominal aortic aneurysm, or certain types of carotid artery disease
The person's risk of developing CHD within 10 years is based on data from the Framingham Heart Study. This 10-year risk is calculated from a formula that takes the following into account:
systolic blood pressure, which is the top number on a blood pressure reading
treatment for high blood pressure
An LDL test may also be ordered to evaluate disorders of the kidney, liver, or thyroid gland.
How is the test performed?
The first step in measuring LDL cholesterol is to take a blood sample. Blood is usually drawn from a vein in the forearm or the hand. To do this, the skin over the vein is cleaned with an antiseptic. Next, a strong rubber tube, or tourniquet, is wrapped around the upper arm. This enlarges the veins in the lower arm by restricting blood flow through them. A very thin needle is gently inserted into a vein and the tourniquet is removed. Blood flows from the vein through the needle and is collected into a syringe or vial. The sample is sent to the lab to be analyzed for LDL cholesterol. After the needle is withdrawn, the puncture site is covered for a short time to prevent bleeding.