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No content on this site, regardless of date, should ever be used as a substitute for direct medical advice from your doctor or other qualified clinician. Certain blood tests require fasting beforehand. If your healthcare provider has instructed you to fast before your upcoming test, it means that you should not eat or drink anything (besides water) for the specified amount of time before having your blood drawn.Understanding why fasting is important and how to properly fast before a blood test can be helpful for eliminating pre-test anxiety and simplifying the testing process. Below, learn how to fast for a blood test correctly to help make sure that your test results are accurate. Why Is Fasting Required Before Blood Tests?Fasting before a blood test helps improve the accuracy and reliability of the test. Accurate test results are a critical component of diagnosing various health conditions and monitoring the effectiveness of treatment plans. Your diet contains a range of nutrients, including carbohydrates, proteins, fats, minerals, and vitamins. When you eat and drink normally, those nutrients are broken down and absorbed into your bloodstream. This can impact the levels of those substances in the blood and skew lab test results. For example, certain methods of diabetes testing measure the patient’s baseline blood sugar levels after a period of fasting. Eating directly before the test will cause the patient’s blood sugar to spike, leading to an inaccurate test result. The patient could be misdiagnosed with prediabetes or diabetes unless their doctor recommends that they complete a second test. Which Blood Tests Require Fasting?Not all lab tests require fasting beforehand, but many of the most common blood tests do. Tests that typically require fasting include:
Can I Drink Water Before a Blood Test?Yes, you can drink water while fasting before a blood test—in fact, drinking plenty of water can help ensure that you receive accurate test results. Dehydration can affect certain blood tests such as cholesterol, electrolyte, and BUN tests. Be sure to stay hydrated before your test by drinking the recommended amount of water for your weight and activity level. Can I Drink Coffee / Alcohol / Juice / Soda / Tea While Fasting?No. Any beverage other than water should not be consumed before a blood test unless approved by your healthcare provider. Alcohol, soda, and juice contain high quantities of sugar, which can interfere with many common test results. Black coffee, tea, and other caffeinated beverages are diuretics, which can have a dehydrating effect and cause test results to be inaccurate. For best results, avoid drinking all non-water beverages for the recommended amount of time before your test. What If I Accidentally Eat or Drink Before My Blood Test?If you have been instructed to fast before your blood test and you accidentally eat or drink something during the fasting window, it is important to notify your healthcare provider or the person drawing your blood. If you don’t, your results could be incorrectly interpreted. It may be possible for your healthcare provider to interpret the non-fasted test results. Most likely, they will instruct you to reschedule the blood test at a time when you will be able to successfully complete the fast before the test. Your physician will let you know the steps you need to take before your blood test, including whether or not fasting is required and for how long. By following all testing instructions and best practices (including how to fast), you can ensure a smooth testing process and the most accurate results. Are you a patient in need of lab testing? Find a convenient testing location and schedule an appointment near you. Can I drink water before a fasting blood test for diabetes?To prepare for a fasting glucose test, you should have nothing to eat or drink (except water) for 8 to 12 hours. Your healthcare provider will tell you how long to fast.
Is 12 hours fasting required for blood sugar test?The most common types of tests that require fasting include: Glucose tests, which measure blood sugar. One type of glucose test is called a glucose tolerance test. For this test you will need to fast for 8 hours before test.
How long should I fast before an A1C blood draw?Health care professionals can use the A1C test alone or in combination with other diabetes tests to diagnose type 2 diabetes and prediabetes. You don't have to fast before having your blood drawn for an A1C test, which means that blood can be drawn for the test at any time of the day.
When is the best time to do a diabetes blood test?Testing is usually recommended before meals and at bedtime if you're taking multiple daily injections. You may need to test only before breakfast and sometimes before dinner or at bedtime if you use just an intermediate- or a long-acting insulin.
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