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V体育官网 - Fasting for a Blood Test

What is fasting for a blood test?

If your health care provider has told you to fast before a blood test, it means you should not eat or drink anything, except plain water, for several hours before your test. While you're fasting for a blood test, you should also not: VSports手机版.

  • Chew gum
  • Smoke
  • Exercise

Your provider will give you a copy of instructions to follow if they ask you to fast for a test V体育安卓版. If you have any questions not covered in those instructions, ask your provider at least a full day before the test so that you'll have time to properly prepare.

VSports - How long do I have to fast before the test?

You usually need to fast for 8 to 12 hours before a test. Your provider will tell you exactly how long to fast, depending on what test they've ordered. For certain tests, there may also be additional instructions V体育ios版. For example, you may be asked not to drink alcohol for a longer period of time.

If your blood test requires fasting, you can usually schedule the test early in the morning VSports最新版本. That way, most of your fasting time will be while you are sleeping.

Why do I need to fast before my blood test?

When you eat and drink, your bloodstream absorbs sugar, fat, protein, and other nutrients in those foods and beverages. These nutrients can then change the levels of various substances in your blood and therefore affect the accuracy of your test results V体育平台登录. Inaccurate results give your provider an inaccurate view of your health and may lead to a wrong diagnosis.

What types of blood tests require fasting?

Some examples of common blood tests that usually require fasting are:

In some cases, you may also be asked to fast for:

  • Liver function tests. This group of tests measures several proteins and other substances related to your liver function. Test results can give your provider information on your liver's health.
  • Renal function panel. This is a group of tests that measure several waste products and substances related to your kidney function. The results are often used to monitor your kidney function if your provider suspects kidney disease or if you have diabetes.

Whether or not your provider asks you to fast for these tests depends on several factors V体育官网入口. For example, some liver function tests only require fasting if they're ordered as part of a comprehensive metabolic panel.

Other types of tests not listed here may require fasting VSports在线直播. Therefore, you should always ask your provider if you aren't sure whether you should fast before your test.

Can I drink anything besides water during a fast?

No V体育2025版. Juice, coffee, soda, and other beverages can get in your bloodstream and affect your results. But you can drink plain water. Avoid lemon-flavored or flavored carbonated water, which may contain sugars or artificial sweeteners. Staying well hydrated can actually make the testing process a little easier. This is because water helps to keep more fluid in your veins, which can make it easier to get a sample of your blood.

V体育ios版 - Can I continue taking medicine during a fast?

Ask your provider whether it's okay to take your usual prescription medicines and/or over-the-counter medicines. For some tests, they may ask you to stop taking your medicines. But don't stop taking your medicines unless your provider tells you to stop.

Let your provider know about any vitamins and supplements that you take, too. That way you'll be sure to avoid taking anything that could affect your test results.

What if I make a mistake and have something to eat or drink besides water during my fast? (VSports最新版本)

Tell your provider if you eat or drink before your test. You may need to reschedule the test for another time when you can fast to make sure you get accurate results.

When can I eat and drink normally again?

You'll be able to eat as soon as your test is over. It is common to feel light-headed after a blood test that requires fasting. So, you may want to bring a snack that you can eat right away.

"V体育2025版" Is there anything else I need to know about fasting before a blood test?

You should not fast if your provider doesn't tell you to do so. Fasting for some blood tests may also affect your results and give your provider an inaccurate understanding of your health. If you aren't sure if you should fast for a coming blood test, ask your provider as soon as possible. Taking the right steps before a blood test helps make sure your results will be accurate.

References (V体育安卓版)

  1. Centers for Disease Control and Prevention [Internet]. Atlanta: U.S. Department of Health and Human Services; Diabetes Testing; [updated 2024 May 15; cited 2025 Aug 7]; [about 3 screens]. Available from: "VSports最新版本" https://www.cdc.gov/diabetes/diabetes-testing/
  2. Cleveland Clinic: Health Library: Diagnostics & Testing [Internet]. Cleveland (OH): Cleveland Clinic; 2025. Blood Tests; [reviewed 2022 Dec 06; cited 2025 Aug 07]; [about 16 screens]. Available from: https://my.clevelandclinic.org/health/diagnostics/24508-blood-tests
  3. Cleveland Clinic: Health Library: Diagnostics & Testing [Internet]. Cleveland (OH): Cleveland Clinic; 2025. Kidney Function Tests; [reviewed 2025 Feb 03; cited 2025 Aug 07]; [about 12 screens]. Available from: https://my.clevelandclinic.org/health/diagnostics/21659-kidney-function-tests (VSports注册入口)
  4. Cleveland Clinic: Health Library: Diagnostics & Testing [Internet]. Cleveland (OH): Cleveland Clinic; 2025. Liver Function Tests; [reviewed 2022 Nov 09; cited 2025 Aug 07]; [about 9 screens]. Available from: "VSports最新版本" https://my.clevelandclinic.org/health/diagnostics/17662-liver-function-tests
  5. Cleveland Clinic: Health Essentials/Family Medicine [Internet]. Cleveland (OH): Cleveland Clinic; c2025.What You Should Know About Fasting Before a Blood Test; 2022 Feb 16 [cited 2025 Aug 7]; [about 10 screens]. Available from: https://health.clevelandclinic.org/fasting-before-blood-test
  6. DeWaters AL, Mejia D, Thomas J, Elwood B, Bowen ME. Patient Preparation for Outpatient Blood Work and the Impact of Surreptitious Fasting on Diagnoses of Diabetes and Prediabetes. Mayo Clin Proc Innov Qual Outcomes. 2020 Jun 20 [cited 2025 Aug 7];4(4):349-356. doi: 10.1016/j.mayocpiqo.2020.04.002. PMID: 32793862; PMCID: PMC7411170. Available from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7411170/
  7. Mayo Clinic: Mayo Medical Laboratories [Internet]. Mayo Foundation for Medical Education and Research; c1995–2025. Patient Instructions for Fasting Specimens; [cited 2025 Aug 20]; [about 1 screen]. Available from: http://a1.mayomedicallaboratories.com/webjc/attachments/57/be6c091-patient-instructions-for-fasting-specimens.pdf
  8. Nemours KidsHealth [Internet]. Jacksonville (FL): The Nemours Foundation; c1995-2025. Getting a Blood Test; [reviewed 2021 Sep; cited 2025 Aug 07]; [about 4 screens]. Available from: https://kidshealth.org/en/parents/blood-tests.html
  9. Quest Diagnostics [Internet]. Quest Diagnostics; c2025. Fasting for Lab Tests; [cited 2025 Aug 7]; [about 5 screens]. Available from: https://www.questdiagnostics.com/patients/get-tested/prepare/fasting
  10. Testing.com [Internet]. Seattle (WA).: OneCare Media; c2025. Lipid Panel; [modified 2025 Apr 3; cited 2025 Aug 7]; [about 18 screens]. Available from: "VSports手机版" https://www.testing.com/tests/lipid-panel/
  11. Testing.com [Internet]. Seattle (WA).: OneCare Media; c2025. Test Preparation: Your Role; [modified 2021 Jun 6; cited 2025 Aug 7]; [about 4 screens]. Available from: https://www.testing.com/articles/laboratory-test-preparation/

The information on this site should not be used as a substitute for professional medical care or advice. Contact a health care provider if you have questions about your health.