5 Facts About Fasting for Lab Tests

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Your doctor writes a prescription for a lab test and tells you that you must fast for it. The result? Your stomach begins to immediately grumble as its way of talking back. We know that delaying that first cup of coffee or bite of breakfast is a challenge, but not so fast! We're about to explain why it's so important to skip that morning meal before a fasting blood test with these five facts.

1. Not all blood tests require fasting.

There are only certain tests that require you to fast for eight to twelve hours before your appointment. This is because for certain tests, the nutrients and ingredients from what you eat or drink (if its anything other than water) is absorbed into your bloodstream and can influence the factors that are being measured in the blood for particular lab tests. In these cases, fasting improves the accuracy of the results and gives your doctor the best picture of your health.

Some of the more common lab tests that require fasting include:

  • Blood glucose and C-peptide testing that checks blood-sugar and insulin levels
  • Lipid profile tests to measure cholesterol, triglycerides and high-density lipoprotein (HDL) levels
  • Vitamin B12 level testing

2. You can drink water (unless otherwise instructed by your doctor)

For most blood tests that require fasting, it's okay to drink water. In fact, water hydrates your veins, which makes them easier to find and to draw blood from. So, it's actually good to drink plenty of water before a blood test. If your doctor recommends a blood test that requires fasting, ask if drinking water is okay. That way, you know for sure.

3. Most of the time, it's advised to take regular medications before a fasting blood test.

Often, it's advised to continue taking your regular medications, even before a fasting blood test. But, its always good to clear this with your doctor, as well as any vitamin or supplements that you take on a daily basis.

4. Once your blood test is complete, eat!

It's a good idea to make your fasting blood test appointment first thing in the morning and bring at least a snack with you. That way, you can have a quick bite ready to enjoy as soon as your blood test is complete.

5. Always call your doctor or lab with any questions about your lab test.

If you have any questions about your test or fasting requirements, call your doctor or lab ahead of time to be prepared. And always be honest about your fasting with your health professionals. The accuracy of your labs guides their very important recommendations and treatment plans, including medication dosages, for example.

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