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Why is fasting important for blood tests?
What blood tests require fasting?
Do blood tests require you to fast?
Apr 16, 2024 · Actually, fasting affects the results of very few blood tests. For example, measurements of kidney, liver, and thyroid function, as well as blood counts, are not influenced by fasting. However, fasting is often recommended before tests for glucose (blood sugar) and triglycerides (part of the cholesterol, or lipid, panel) to provide the most ...
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With certain blood tests, you may be instructed to fast for up to eight hours before your appointment. Fasting before a blood draw means you don’t eat or drink anything except water. Don’t wait until the day of your blood draw to ask if you should fast. That could cause your appointment to be rescheduled.
- What is fasting for a blood test?
- How long do I have to fast before the test?
- Why do I need to fast before my blood test?
- What types of blood tests require fasting?
- Can I drink anything besides water during a fast?
- Can I continue taking medicine during a fast?
- What if I make a mistake and have something to eat or drink besides water during my fast?
- When can I eat and drink normally again?
- Is there anything else I need to know about fasting before a blood test?
- References
If your health care provider has told you to fast before a blood test, it means you should not eat or drink anything, except water, for several hours before your test. While you're fasting for a blood test, you also should not:
•Chew gum
•Smoke
•Exercise
You usually need to fast for 8 to 12 hours before a test, but your provider will tell you exactly how long to fast. For certain tests, 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. That way, most of your fasting time will be while you are sleeping.
When you eat and drink, your bloodstream absorbs sugar, fat, protein, and other nutrients in those foods and beverages. That could affect the results of certain blood tests and lead to the wrong diagnosis.
Some examples of common blood tests that usually require fasting are:
•Blood sugar (glucose) tests. These tests measure the level of blood glucose in a sample of your blood. They are used to help diagnose and monitor diabetes, prediabetes, and gestational diabetes (diabetes that starts during pregnancy). Not all blood glucose tests require fasting, so ask your provider if you need to fast for your test.
•Cholesterol levels tests (lipid panel). These tests measure the level of fats, called lipids, in your bloodstream, including cholesterol and triglycerides. The test results help show your risk of getting heart disease.
•Basic metabolic panel (BMP). This is a group of tests that measures several natural chemicals in your blood. The results give your provider information about how well your organs are working, including your heart, kidneys, and liver.
No. Juice, coffee, soda, and other beverages can get in your bloodstream and affect your results. But you can drink water. It's good to drink water before a blood test. It helps keep more fluid in your veins, which can make it easier to get a sample of your blood.
Ask your provider whether it's okay to take your usual prescription medicines and/or over-the-counter 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.
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.
You'll be able to eat as soon as your test is over. You may want to bring a snack with you, so you can eat right away.
If you don't know whether you should fast for your blood test, ask your provider at least a day before your test so you'll have time enough time to fast.
If you fast before a test when you don't need to, that may affect your results, too. That's why it's important to find out for sure whether you need to fast.
1.Allina Health [Internet]. Minneapolis: Allina Health; Fasting for a Blood Test; [cited 2022 Jul 14]; [about 1 screen]. Available from: https://www.allinahealth.org/-/media/allina-health/files/15008fastingpt.pdf
2.Centers for Disease Control and Prevention [Internet]. Atlanta: U.S. Department of Health and Human Services; Diabetes Home: Getting Tested; [updated 2021 Aug 10; cited 2022 Jul 14]; [about 3 screens]. Available from: https://www.cdc.gov/diabetes/basics/getting-tested.html
3.Cleveland Clinic: Health Essentials/Family Medicine [Internet]. Cleveland (OH): Cleveland Clinic; c2022.What You Should Know About Fasting Before a Blood Test; 2022 Feb 16[cited 2022 Jul 25]; [about 6 screens]. Available from: https://health.clevelandclinic.org/fasting-before-blood-test/
4.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 2022 Jul 25];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/
5.National Heart, Lung, and Blood Institute [Internet]. Bethesda (MD): U.S. Department of Health and Human Services; Blood Tests; [updated 2022 Mar 24; cited 2022 Jul 25]; [about 8 screens]. Available from: https://www.nhlbi.nih.gov/health-topics/blood-tests
6.Quest Diagnostics [Internet]. Quest Diagnostics; c2022. Fasting for Lab Tests; [cited 2022 Jul 14]; [about 3 screens]. Available from: https://www.questdiagnostics.com/patients/get-tested/prepare/fasting
Oct 3, 2019 · The do’s and don’ts of fasting before routine bloodwork. October 3, 2019. Mary Leigh Meyer. Healthy Living, Medicine, Show on VR homepage. Occasionally, your primary care provider may ask you to fast prior to your appointment, and a physician explains what to do. A few vials full of blood.
3 days ago · By Angela Ryan Lee, MD. Updated on May 24, 2024. Medically reviewed by Steffini Stalos, DO. Print. View All. Fasting Tests. Duration. Why It's Needed. How to Fast. What to Do If You Eat. End of Fasting. FAQ. You may have to fast—avoiding anything but water—for eight to 12 hours before a blood test.
Nov 8, 2022 · Fasting is important for certain types of blood tests. This is because the foods you usually eat and drink absorb into your bloodstream, affecting the test results. For many blood tests, fasting is not necessary. However, for testing glucose and cholesterol, fasting is important for accurate results and diagnosis.
Jun 9, 2023 · Fasting before blood work means you shouldn’t eat or drink anything except water for at least eight hours before a blood test. For some tests, you may need to fast for 12 hours. Ask your health care provider how long to fast before your blood test if you’re unsure.
