Ask your doctor if you need to fast before a blood test

If your health care provider 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. When you eat and drink normally, those foods and beverages are absorbed into your bloodstream. That could affect the results of certain types of blood tests.

Blood tests that require fasting

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. When you arrive at the lab, you will:
• Have your blood tested
• Drink a special liquid containing glucose
• Have your blood re-tested one hour later, two hours later and possibly three hours later

Lipid tests, which measure triglycerides, a type of fat found in the bloodstream, and cholesterol, waxy, fat-like substance found in your blood and every cell of your body.

How long should you fast before a test?

You usually need to fast for 8–12 hours before a test. Most tests that require fasting are scheduled for early in the morning. That way, most of your fasting time will be overnight.

Are you allowed to drink anything besides water during a fast?

No. Juice, coffee, soda, and other beverages can get in your bloodstream and affect your results. In addition, you should not:
• Chew gum
• Smoke
• Exercise
These activities can also 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 draw blood.

Should you continue taking medicine during a fast?

Ask your health care provider. Most of the time it’s OK to take your usual medicines, but you may need to avoid certain medicines, especially if they need to be taken with food.

What happens if you make a mistake and have something to eat or drink besides water during fast?

Tell your health care provider before your test. He or she can reschedule the test for another time when you are able to complete your fast.

When can you eat and drink normally again?

As soon as your test is over. You may want to bring a snack with you, so you can eat right away.

Is there anything else you need to know about fasting before a blood test?

Be sure to talk to your health care provider if you have any questions or concerns about fasting.
You should talk to your provider before taking any lab test. Most tests don’t require fasting or other special preparations. For others, you may need to avoid certain foods, medicines, or activities. Taking the right steps before testing helps ensure your results will be accurate.

What if you do not have a doctor?

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