Low density lipoprotein
This is a test that measures the amount of low-density lipoprotein (LDL) cholesterol in serum.
Cholesterol levels are determined through chemical analysis of a blood sample taken from a finger prick or from a vein in the arm. Home cholesterol kits, first approved in 1993, test only for total cholesterol levels but are as accurate as tests done in a doctor’s office, says Steven Gutman, M.D., director of FDA’s division of clinical laboratory devices.
“These tests can give a consumer very valuable information when screening for High cholesterol,” he says. “But they shouldn’t be considered substitutes for a test conducted in a doctor’s office.” He adds that if test results are elevated, consumers should see a doctor right away for a more refined blood analysis. The National Cholesterol Education Program considers cholesterol testing in a doctor’s office to be the preferred way because the patient can get advice immediately about the meaning of the results and what to do.
Besides determining total cholesterol levels, doctors often order a lipoprotein profile that shows the amounts of LDL, HDL, and another type of blood fat called triglycerides. This information gives doctors a better idea of heart disease risk and helps guide any treatment.
What do my cholesterol numbers mean?
Talk to your health care provider about the results of your cholesterol test. The following guidelines come from the National Cholesterol Education Program (NCEP) of the National Heart, Lung, and Blood Institute, National Institutes of Health. Cholesterol levels are measured in milligrams (mg) of cholesterol per deciliter (dL) of blood.
- Total cholesterol level - a level of less than 200 mg/dL is desirable. But even levels of 200-239 mg/dL (borderline high) can increase your risk of Heart disease.
Total Cholesterol Level Category Less than 200 mg/dL Desirable 200 - 239 mg/dL Borderline high 240 mg/dL and above High
LDL (bad) cholesterol - a level of 160 mg/dL or above is high. Work with your health care provider to determine a goal LDL level that’s best for you.
LDL Cholesterol Level Category Less than 100 mg/dL Optimal 100-129 mg/dL Near optimal/above optimal 130-159 mg/dL Borderline high 160-189 mg/dL High 190 mg/dL and above Very high
HDL (good) cholesterol - a level of 60 mg/dL or more is good and helps to lower your risk for Heart disease. Remember that HDL (good) cholesterol protects against Heart disease, so for HDL, higher numbers are better. A level less than 40 mg/dL is low and increases your risk for developing Heart disease.
- Triglyceride levels - can also raise your risk for Heart disease. Levels that are borderline high (150-199 mg/dL) or high (200 mg/dL or more) may need treatment in some people.
How the test is performed
Adult or child:
Blood is drawn from a vein (venipuncture), usually from the inside of the elbow or the back of the hand. The puncture site is cleaned with antiseptic, and a tourniquet (an elastic band) or blood pressure cuff is placed around the upper arm to apply pressure and restrict blood flow through the vein. This causes veins below the tourniquet to distend (fill with blood). A needle is inserted into the vein, and the blood is collected in an air-tight vial or a syringe. During the procedure, the tourniquet is removed to restore circulation. Once the blood has been collected, the needle is removed, and the puncture site is covered to stop any bleeding.
Infant or young child:
The area is cleansed with antiseptic and punctured with a sharp needle or a lancet. The blood may be collected in a pipette (small glass tube), on a slide, onto a test strip, or into a small container. Cotton or a bandage may be applied to the puncture site if there is any continued bleeding.
How to prepare for the test
Fasting for 12 hours may be advised. The health care provider may advise you to withhold drugs that may affect the test (see special considerations).
Infants and children:
The physical and psychological preparation you can provide for this or any test or procedure depends on your child’s age, interests, previous experiences, and level of trust. For specific information regarding how you can prepare your child, see the following topics as they correspond to your child’s age:
- Infant test or procedure preparation (birth to 1 year)
- Toddler test or procedure preparation (1 to 3 years)
- Preschooler test or procedure preparation (3 to 6 years)
- School age test or procedure preparation (6 to 12 years)
- Adolescent test or procedure preparation (12 to 18 years)
How the test will feel
When the needle is inserted to draw blood, some people feel moderate pain, while others feel only a prick or stinging sensation. Afterward, there may be some throbbing.
Why the test is performed
This test is usually performed as part of an evaluation of coronary risk factors.
Cholesterol is an important normal constituent of the body. It is part of the structure of cell membranes, bile acids, and steroid hormones. Since cholesterol is water insoluble, most cholesterol is carried in the blood by lipoproteins (large protein-like molecules, including chylomicrons, VLDL, LDL, and HDL). Chylomicrons are lipoproteins that are present shortly after a meal, but disappear within about 2 hours in “normal” people.
The main function of LDL seems to be to carry cholesterol to various tissues throughout the body. The laboratory actually measures the cholesterol portion of the LDL molecule, rather than the actual concentration of LDL in the blood. This is also true for high density lipoprotein (HDL) and very low density lipoprotein (VLDL). The total cholesterol level is the sum of LDL, HDL, and VLDL cholesterol.
Excess cholesterol in the blood has been correlated with cardiovascular disease. LDL is sometimes referred to as “bad” cholesterol because elevated levels of LDL correlate most directly with coronary heart disease.
According to the National Heart, Lung, and Blood Institute, your LDL cholesterol level is a better indicator of your risk for a heart attack and stroke than total cholesterol. The lower your LDL, the lower your risk for heart disease or stroke.
A healthy LDL level is one that falls in the optimal or near-optimal range.
- Optimal: Less than 100 mg/dL
- Near Optimal: 100-129 mg/dL
- Borderline High: 130-159 mg/dL
- High: 160-189 mg/dL
- Very High: 190 mg/dL and higher
What abnormal results mean
High levels of LDL may be associated with:
- Increased risk of atherosclerotic heart disease
- Familial hyperlipoproteinemia
Lower-than-normal levels of LDL may be caused by:
Additional conditions under which the test may be performed:
What the risks are
- Excessive bleeding
- Fainting or feeling light-headed
- Hematoma (blood accumulating under the skin)
- Infection (a slight risk any time the skin is broken)
- Multiple punctures to locate veins
Drugs that can increase lipoprotein levels include aspirin, oral contraceptives, phenothiazines, corticosteroids, and sulfonamides.
Veins and arteries vary in size from one patient to another, and from one side of the body to the other. Obtaining a blood sample from some people may be more difficult than from others.
by Martin A. Harms, M.D.
All ArmMed Media material is provided for information only and is neither advice nor a substitute for proper medical care. Consult a qualified healthcare professional who understands your particular history for individual concerns.