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- Fasting for blood work means you don't eat or drink anything but water for 8-12 hours before you have a blood test. You also need to avoid chewing gum, smoking, exercising, and taking certain medications and supplements. Your doctor will ask you to do this for certain blood tests because foods and drinks can affect your results.
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Jul 29, 2024 · 4 min read. What Is Considered Fasting for Blood Work? Fasting for blood work means you don't eat or drink anything but water for 8-12 hours before you have a...
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Aug 19, 2024 · Blood glucose tests, particularly the fasting plasma glucose test, are critical for diagnosing and managing diabetes. When testing for diabetes or prediabetes, fasting ensures that your blood sugar level is measured at a baseline state, unaffected by recent food intake.
Feb 16, 2022 · How long do you have to fast before a blood test? Can you drink water? What about black coffee? Our expert answers questions about fasting before a blood test.
- Overview
- Which blood tests require you to fast?
- How long should you fast before a blood test?
- Can you drink coffee if you’re fasting before a blood test?
- Can you drink alcohol if you’re fasting before a blood test?
- Can you drink water before a fasting blood test?
- What else should I avoid before a fasting blood test?
- What if your child needs to fast before a blood test?
- What about fasting for a blood test during pregnancy?
- Q&A: What happens if you don’t fast before a blood test?
Fasting before certain blood tests is important to help make sure that your test results are accurate.
Some blood tests require you to fast beforehand. In these cases, your doctor will instruct you not to eat or drink anything, except water, in the hours leading up to the test.
Not all blood tests will require you to fast beforehand. Blood tests that you will likely need to fast for include:
•blood glucose test
•liver function test
•iron level blood test
•basic metabolic panel
•renal function panel
Tip
Schedule your test as early in the day as possible. The hours you spend sleeping count as part of the fasting period, as long as you don’t break your fast with coffee or food once you’re awake. Was this helpful?
Coffee can interfere with blood test results. That’s because it contains caffeine and soluble plant matter, which might skew your test results.
Coffee is also a diuretic, which means it will increase how much you pee. This can have a dehydrating effect. The less hydrated you are, the harder it can be for a healthcare professional to find a vein for the blood draw. This can make the test harder or more stressful for you.
Recent research suggests that black coffee may not have much of an effect on certain tests, but more research is needed.
Tea and energy drinks are also off-limits before a fasting blood test.
Some blood tests, such as those that assess liver health or triglyceride levels, may require you not to drink alcohol for 24 hours. Alcohol can affect your enzyme, glucose, and lipid levels.
If you have any concerns about alcohol consumption, discuss them with your doctor when you schedule your test.
It’s fine to drink water before a blood test unless your doctor instructs you otherwise. This is different from some surgical procedures, which may require you to have a totally empty stomach.
Tap or bottled water are both OK, but leave the squeeze of lemon for another time. Seltzer and club soda are off-limits. You shouldn’t consume carbonated beverages, flavored or otherwise, during a fast.
If you have to fast before a blood test, you should also avoid the following:
•Chewing gum: Even sugar-free gum can affect several key results, according to 2020 research.
•Smoking: Traces of nicotine can stay in your blood for up to 5 days. Smoking can also affect lipoprotein levels in your blood. Check with your doctor about whether you’ll need to refrain from smoking, vaping, or chewing tobacco beforehand and for how long.
•Exercise: Blood tests provide the most accurate results when you’re at rest. Some experts recommend refraining from strenuous exercise for at least 24 hours before a blood test.
Tips for parents
•Schedule your child’s blood test as early in the day as possible. •Distract, distract, distract: The hours leading up to the test may be the time to give in and let them watch a nonstop hour of goofy cartoons on TV or play with your tablet. •Pack a snack for them to devour as soon as the test is done. •If they manage to sneak a snack when you’re not looking, it’s better to reschedule than to get inaccurate readings. Was this helpful?
Some standard tests during pregnancy may require you to fast beforehand. Your doctor will advise you how to prepare for each test.
Fasting is usually safe if you’re pregnant, provided you’re in good health and aren’t having a high risk pregnancy. For your overall comfort, your doctor may advise you to drink extra water or to remain indoors, especially if the weather is very hot or humid.
Fasting may increase heartburn in some pregnant people. Let your doctor know if you experience uncomfortable or concerning symptoms while waiting to have your blood drawn.
If you’re seeing a doctor other than your obstetrician-gynecologist, be sure to let them know about your pregnancy before your blood test.
Q:
What happens if you don’t fast before a blood test? Should you still do the test? Anonymous
A:
If you don’t fast before a test that requires it, the results may not be accurate. If you forget and eat or drink something, call your provider and ask if the test can still be done. Some tests can be analyzed with a notation that it isn’t fasting, and results may vary. The main thing is to be honest. If you had a snack, a cup of coffee, or even a full breakfast, tell the technician when you have your blood drawn. They should make a note so that the results are reviewed with the food intake as a variable. And if fasting is an absolute must for meaningful results, they should stop and reschedule your blood draw. Deborah Weatherspoon, PhD, RN, CRNAAnswers represent the opinions of our medical experts. All content is strictly informational and should not be considered medical advice. Was this helpful?
- Corey Whelan
Jul 15, 2024 · Fasting before a blood test means that a person should not eat or drink anything other than water. Typically, if a blood test requires fasting, doctors schedule it for the...
- Lana Burgess
Nov 9, 2022 · Some blood tests require you to fast beforehand. This means you cannot eat or drink anything other than water for a certain time. Learn more here.
People also ask
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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.
