An LDL test measures the level of low-density lipoprotein (LDL) in the blood. LDL is known as "bad" or "lethal" cholesterol, because higher levels of it in the blood correlate with a higher risk of heart disease and stroke. This is because LDL is the type of fat that tends to help clog up arteries. The LDL test is usually done as part of a lipid profile test that also includes total cholesterol, HDL, and triglycerides.
Who is a candidate for the test?
An LDL test may be used to evaluate a person's risk for artherosclerosis. 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 (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:
- cigarette smoking
- HDL cholesterol
- systolic blood pressure, which is the top number on a blood pressure reading
- total cholesterol
- treatment for high blood pressure
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 After the needle is withdrawn, the puncture site is covered for a short time to prevent bleeding.
What is involved in preparation for the test?
An LDL test is generally done after the individual has fasted overnight.
What do the test results mean?
LDL results in healthy
adults are evaluated as follows:
- optimal is less than 100 milligrams per deciliter, or mg/dL
- near optimal/above optimal is 100 to 129 mg/dL
- borderline high is 130 to 159 mg/dL
- high is 160 to 189 mg/dL
- very high is 190 mg/dL or greater
If an individual has certain other risk factors, LDL goals are more strict. LDL goals for these groups are as follows:
- less than 100 mg/dL for people with CHD and CHD risk equivalents
- less than 130 mg/dL for individuals with two or more risk factors
- less than 160 mg/dL for people with 0 to 1 risk factor
Abnormally high levels of LDL may indicate the following:
- cirrhosis of the liver
- diet high in cholesterol, saturated fats, calories, or trans fats
- familial hyperlipidemia, a condition in which having high blood lipids runs in a family
- hypothyroidism, or an underactive thyroid gland
- nephrotic syndrome, which is a kidney disease resulting in loss of protein in the urine
Abnormally low levels of LDL may indicate the following:
- hyperthyroidism, or an overactive thyroid gland
- malabsorption, or inadequate absorption of nutrients from the intestines