A few vials full of blood

The do’s and don’ts of fasting before routine bloodwork

Occasionally, your primary care provider may ask you to fast prior to your appointment, and a physician explains what to do
October 3, 2019

If you have ever visited a primary care provider, then you have likely been asked to fast before getting routine bloodwork. To learn more, we asked an expert about what you can and cannot do while fasting.

“Some of those blood tests, in either screening for chronic conditions or in monitoring of your chronic conditions, may be affected by some of the nutrients that are in food or drink,” said Jason McKnight, MD, MS, family medicine physician at Texas A&M Health Family Care and clinical assistant professor at the Texas A&M College of Medicine.

McKnight also mentioned the food or drinks you consume the day or night before a blood test does not impact your test results, unlike what you eat or drink the morning of your test.

“It’s recommended that you avoid coffee and other liquids during your fast,” McKnight said. “You never know what kind of nutrient value or additives are in those liquids, so it’s best to just stick with sips of water, unless otherwise cleared by your physician or provider.”

On a similar note, he says to avoid vitamins and snacks, but not to stop any prescribed medications, unless otherwise instructed by your provider. If you have any questions about whether you need to fast and for how long, ask your health care provider the day before your bloodwork.

For Vital Record, this is Mary Leigh Meyer.

— Mary Leigh Meyer

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