Measuring the amount of cholesterol in your blood is one important step in determining your risk of coronary artery disease and its complications, including heart attack. High cholesterol increases your risk of coronary artery disease. However, cholesterol levels can be lowered, making your risk for developing the disease less. Determining your cholesterol level is done by a simple blood test. It's important to know how to prepare for your lab test, so that the results will be accurate.
Cholesterol
Cholesterol is a fatty substance that helps cells to function properly. However, if the amount of cholesterol in the body exceeds what the cells need to function, it can build up in and clog blood vessels, especially the blood vessels that feed the heart. Coronary arteries when blocked by cholesterol and calcium become hard and narrow. In combination with other factors, such as diabetes or high blood pressure, these narrowed vessels can restrict the flow of blood to the heart and cause a heart attack.
Testing
Testing the amount of cholesterol in the blood is performed by drawing blood from a blood vessel and analyzing it in the laboratory. Different types of cholesterol testing can be performed on the blood sample. Most often, the total amount of cholesterol in the blood is examined, as well as its subtypes: HDL -- high-density lipoprotein -- the "good" cholesterol and LDL-- low-density lipoprotein, the "bad" cholesterol. Other types of fat in the blood may also be analyzed, such as triglycerides. All of these tests, in combination, are called a "lipid profile," and will give a very accurate picture of your risk of heart disease.
Screening
The amount of cholesterol and fat in your blood is affected by a number of factors; one of these factors is your diet. The results of some of the tests used to determine the amount of cholesterol and fat in the blood are affected by the foods you eat. Sometimes a doctor will request that your blood be drawn to look at the amount of total cholesterol and/or HDL -- a screening test. If the results of the screening test are abnormal, then he may request a complete lipid profile
If your blood is being drawn to determine only total cholesterol and/or HDL, such as for a screening test, then you don't need to fast. The measurement of total cholesterol and HDL will not be affected by eating before the test.
Lipid Profile
Most often, however, your doctor will request that your blood be drawn for a lipid profile: the combination of tests that measures total cholesterol, its subtypes, and other fats. Although the results of your total cholesterol test and HDL are not affected by food, the other parts of the lipid profile -- determination of LDL, and triglycerides -- is markedly affected. The results of these tests will be inaccurate if you eat before the test.
Recommendations
The recommendation from the National Cholesterol Education Program is that you fast -- refrain from eating -- for 9 to 12 hours before having your blood drawn for a lipid profile. Fasting will allow the fat and cholesterol from a meal to be removed from the bloodstream; this will give the most accurate test results. These results will give your doctor a good picture of your risk of heart disease, in combination with other factors, including your family history and lifestyle. By knowing your risk, you and your doctor can make a plan to reduce this risk.
References
- MedlinePlus: Cholesterol Test
- National Heart Lung and Blood Association: Cholesterol
- "Clinical Diagnosis and Management by Laboratory Methods, 20th Edition"; John Bernard Henry, MD; 2001.
