People getting blood tests to check their cholesterol levels are generally told to fast for 9 to 12 hours before the blood draw, according to the American Heart Association. That's an annoyance that can often lead to canceled and postponed test appointments when patients balk at the prospect of a missed morning coffee or a too-late lunch. However, a recent Canadian study published in the Archives of Internal Medicine suggests that, for many people, eating before the test does not impact the results enough to affect the interpretation.
"Although current guidelines recommend measuring lipid levels in a fasting state, recent studies suggest that non-fasting lipid profiles change minimally in response to food intake and may be superior to fasting levels in predicting adverse cardiovascular outcomes," says Davinder Sidhu, M.D., of the University of Calgary, one of the lead authors of the study.
Lipid tests – which evaluate total cholesterol, high density lipoprotein (HDL) cholesterol, low density lipoprotein (LDL) cholesterol, and triglycerides – are important because high blood cholesterol is a major risk factor for heart disease and stroke. Cholesterol is a fat-like substance found in the blood and if there is too much LDL cholesterol, it can build up on artery walls. Over time, that causes arteries to narrow and slows down or blocks blood flow to the heart, which can cause chest pain or a heart attack. Because high cholesterol itself doesn't cause symptoms, knowledge of cholesterol levels is important as an incentive for people to lower high levels through exercise, medicine, or both.
Currently, the National Cholesterol Education Program, based at the National Institutes of Health, recommends that all adults age 20 or older have a fasting lipoprotein profile (cholesterol checkup) once every five years. Physicians may recommend more frequent tests if:
- Your total cholesterol is 200 mg/dL or more.
- You are a man over age 45 or a woman over age 50.
- Your HDL cholesterol is less than 40 mg/dL.
- You have other risk factors for heart disease and stroke, such as smoking cigarettes.
For the study, the researchers gathered laboratory data for 209,180 men and women who reported fasting anywhere from under one hour to 16 hours. These self-reported fasting times were stratified into hourly intervals and the average lipid values were determined for each interval. The researchers found little difference in the average lipid values at different fasting times. Levels differed less than 2 percent for total cholesterol and HDL cholesterol, less than 10 percent for LDL cholesterol, and less than 20 percent for triglycerides. "This finding suggests that fasting for routine lipid level determinations is largely unnecessary," according to the authors.
In the same issue of the journal in which the new study was published, several heart disease experts weighed in and generally support the idea of eliminating fasting before the tests. J. Michael Gaziano, M.D., M.P.H., Chief of the Division of Aging at Brigham and Women's Hospital in Boston, says that the key reasons cholesterol checks are done are for total cholesterol and HDL results. He noted the "incremental gain in information of a fasting profile is exceedingly small for total and HDL cholesterol values and likely does not offset the logistic impositions placed on our patients, the laboratories, and our ability to provide timely counseling to our patients." Gaziano added that in his opinion, the convenience factor "tips the balance toward relying on non-fasting lipid profiles as the preferred practice."
Amit V. Khera, M.D. and Samia Mora, M.D., M.H.S. of Brigham and Women's Hospital and Harvard Medical School said they think it's reasonable to consider eliminating fasting before lipid tests for most people who are getting routine tests. However, they suggested fasting may be indicated in order to get the most accurate results for people with high triglycerides (greater than 400 mg/dL) and in patients at high risk for heart disease, such as someone with diabetes. They also noted that "Additional prospective studies that directly compare the association of fasting and non-fasting lipid levels with cardiovascular outcomes in the same individuals would be informative."
New guidelines on cholesterol testing from the National Heart Lung and Blood Institute are expected later this year and it remains to be seen whether recommendations on fasting before lipid tests will change. In the meantime, follow your health care provider's instructions on fasting when having your lipid levels checked.
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Sidhu D, Naugler C. Fasting Time and Lipid Levels in a Community-Based Population. Arch Intern Med. 2012;172(22):1707-1710. Available online at http://archinte.jamanetwork.com/article.aspx?articleid=1391022 through http://archinte.jamanetwork.com. Accessed January 29, 2013.
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Khera A, Mora S. Fasting for Lipid Testing: Is It Worth the Trouble? Comment on "Fasting Time and Lipid Levels in a Community-Based Population," Arch Intern Med. 2012;172(22):1710-1711. Available online at http://archinte.jamanetwork.com/article.aspx?articleid=1391005 through http://archinte.jamanetwork.com. Accessed January 29, 2013.
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