Measuring levels of various blood fats, or lipids, in a blood sample can provide important information about the condition of arteries in the body (as well as the presence of liver disease and other conditions). The underlying cause of coronary artery disease (CAD) and most other cardiovascular diseases is atherosclerosisthe narrowing of large arteries by plaques made up of lipids such as cholesterol, as well as smooth muscle cells, collagen and other proteins, and calcium deposits. A cholesterol test may contain the following components.
Total cholesterol. The accumulation of the lipid cholesterol on artery walls plays a primary role in the development of atherosclerosis. Cholesterol is carried through the bloodstream on proteins, called lipoproteins, that are named according to their density properties. Total cholesterol levels include both LDL and HDL cholesterol.
LDL cholesterol. Most cholesterol is transported on low-density lipoprotein, and is thus termed LDL cholesterol. Because LDL cholesterol is the major contributor to atherosclerosis and the most important risk factor for CAD, it is sometimes known as "bad" cholesterol.
HDL cholesterol. Transported on high-density lipoprotein, HDL cholesterol helps to protect against atherosclerosis by removing cholesterol from artery walls and returning it to the liver for disposal. Thus, HDL cholesterol is commonly known as "good" cholesterol; high HDL levels may help to offset the negative impact of high total and LDL cholesterol levels.
Triglycerides. Another major blood lipid that is primarily carried through the bloodstream on very-low density lipoprotein (VLDL), triglycerides serve as a storage source for energy. High levels also contribute to atherosclerosis, and are almost always accompanied by low HDL cholesterol levels.
Purpose of the Cholesterol Test
- To evaluate the risk of cardiovascular disease (particularly CAD)
- To monitor lipid levels in people with known cardiovascular disease
- To confirm a diagnosis of nephrotic syndrome (a kidney disorder), inflammation of the pancreas (pancreatitis), liver disease, and overactive or underactive thyroid gland (hyper- or hypothyroidism); all of these conditions can affect fat metabolism and are characterized by elevated blood lipid levels
- To determine risk of heart attack or stroke caused by blockage of blood vessels or hardening of the arteries (atherosclerois)
- To screen for high cholesterol in adults and children
- To monitor cholesterol levels in people who are being treated for high cholesterol
- To help evaluate the patient’s metabolism of fat
- To diagnose inflammation of the pancreas (pancreatitis), liver disease, or thyroid disorders
Who Performs Cholesterol Test
- A phlebotomist, nurse or a technician
Special Concerns about Cholesterol Test
- The results of this test may be affected by pregnancy, menopause, a wide variety of medications, smoking, current illness, recent surgery, alcohol, flare-up of arthritis, and failure to follow pre-test dietary restrictions.
- HDL levels vary according to age and gender.
Before the Cholesterol Test
- Report to your doctor any medications, herbs, or supplements you are taking. You may be advised to discontinue certain of these agents before the test.
- Since dietary intake affects cholesterol levels, be sure to follow your typical diet for at least a week before the test to maximize the accuracy of results.
- Do not consume alcohol for 24 hours before the test.
- Your doctor will instruct you to avoid eating or drinking anything for 9 to 12 hours before the test (water is permitted). For cholesterol testing, the last meal before the fast should be a low-fat one.
- If HDL cholesterol is being measured, you should also avoid exercise for 12 to 14 hours.
What You Experience
- A sample of your blood is drawn from a vein, usually in your arm, and sent to a laboratory for analysis.
Risks and Complications of the Cholesterol Test
After the Cholesterol Test
- Immediately after blood is drawn, pressure is applied (with cotton or gauze) to the puncture site.
- You may resume your normal diet and any medications withheld before the test.
- Blood may collect and clot under the skin (hematoma) at the puncture site; this is harmless and will resolve on its own. For a large hematoma that causes swelling and discomfort, apply ice initially; after 24 hours, use warm, moist compresses to help dissolve the clotted blood.
Results of Cholesterol Test
- Chemical tests are performed to measure lipids levels in your blood sample.
- The National Cholesterol Education Program (NCEP) recommends that total cholesterol levels be kept below 200 milligrams per deciliter (mg/dL).
- LDL cholesterol should ideally be kept below 100 mg/dL; between 100 and 129 mg/dL is classified as near or above optimal; between 130 and 159 mg/dL is borderline high; and 160 mg/dL and over is considered high.
- HDL cholesterol levels of less than 40 mg/dL are considered a risk factor for CAD. On the other hand, levels of 60 mg/dL or higher are considered protective against CAD.
- A normal triglyceride level is defined as less than 150 mg/dL; between 150 and 199 mg/dL is considered borderline high; between 200 and 499 mg/dL is classified as high; and 500 mg/dL or above is labeled very high.
- If this test was performed to assess CAD risk and your lipid levels are high, your doctor will set target levels and prescribe lifestyle measures (such as diet and exercise) and/or lipid-lowering medications to achieve them.
- If this test was done for another reason, your doctor will consider your lipid levels along with your history, your symptoms, and the results of other tests in order to make a diagnosis.
The Johns Hopkins Consumer Guide to Medical Tests
Simeon Margolis, M.D., Ph.D., Medical Editor
Updated by Remedy Health Media