July 20, 2018
Nurse prepare drawing blood sample from arm patient for blood test

Do You Need to Fast Before a Cholesterol Test?

by Berkeley Wellness  

If you’re scheduled for a blood cholesterol test, there’s a good chance you have been told not to eat or drink anything (except water) for 9 to 12 hours beforehand. Is that really necessary? New international recommendations say you can forgo the fast. Technically called a lipid panel, the testing includes measurements of total cholesterol, LDL (“bad”) cholesterol, HDL (“good”) cholesterol, and triglycerides (fats in the blood). These numbers help assess cardiovascular risk.

Here’s why fasting has generally been advised: Total cholesterol and HDL can be measured fairly accurately without fasting, but triglycerides can vary depending on whether you have eaten recently—in particular a fatty meal—or not. In addition, LDL is not usually measured directly but rather is roughly estimated using an equation that includes triglycerides: LDL = total cholesterol – HDL – (triglycerides ÷ 5). If you don’t fast, your triglyceride measurement could be higher and your LDL lower.

And here’s why you don’t have to fast (with some caveats): The differences in results between fasting and non-fasting tests are not clinically significant, according to a joint consensus statement issued by the European Atherosclerosis Society and the European Federation of Clinical Chemistry and Laboratory Medicine. The committee behind it—which included medical experts from eight European countries, the U.S., and Australia—based the recommendations on several large population studies that compared results under fasting and non-fasting conditions. Not fasting was associated with an LDL level only 8 points lower at most, and triglycerides 26 points higher. What’s more, non-fasting tests were deemed as good at predicting cardiovascular events as fasting tests. The guidelines were published in the European Heart Journal in April.

The committee concluded that “non-fasting blood samples can routinely be used for assessment of plasma lipid profiles in most situations.” Non-fasting tests have been the norm in Denmark since 2009, while the U.K. has endorsed them since 2014. In its last update of joint guidelines in 2013, the American College of Cardiology and American Heart Association said that fasting is “preferred” for initiating and monitoring statin therapy in patients (but not mandatory).

The caveats: These recommendations apply largely to routine screening, not necessarily if you are being evaluated for statin therapy, are about to start other medication that can affect blood lipids, or have established high triglycerides or certain other medical conditions. And the new guidelines stress that if triglycerides are found to be high (above 440) on a non-fasting test, a fasting test should then be considered. You may also need to fast if you are having other blood work done at the same time, such as a blood glucose test.

Bottom line: Talk to your doctor about whether there is a genuine reason to fast before your next cholesterol test, which is generally recommended every five years for adults ages 40 to 75. You may need to be tested more or less often depending on your cardiac risk factors.

Also see:10 Common Cholesterol Questions.