How long must you fast for blood work

Some blood tests require you to fast before you have them done. Typically, this means not eating or drinking anything but water. It is important to follow all the instructions given by your doctor to ensure the most accurate test results.This article will discuss what blood tests require fasting and why it is necessary. It will also answer some questions people frequently ask about fasting before a blood test.

What blood tests require fasting?

If your doctor recommends a fasting blood test, they expect you not to eat or drink for a certain amount of time before.

The most common blood tests that require fasting are:

• Glucose test: Glucose is your blood sugar. A fasting blood sugar (glucose) test is necessary to diagnose diabetes. With this test, your doctor can see if your overnight blood sugar levels fall within the range of diabetes.
• Lipid tests: A lipid test measures the triglycerides and cholesterol in your blood. Triglycerides are a type of fat in your bloodstream. Cholesterol is a fat-like substance in both your blood and every cell in your body. High triglycerides and low-density lipoprotein (LDL) cholesterol levels may increase your risk of heart disease. Read more about high cholesterol.
• Iron tests: Iron blood tests check for conditions like iron deficiency anemia. Iron is an essential mineral for making red blood cells.

Why is fasting necessary?

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.

Follow all instructions your doctor provides to ensure the testing is the most effective.

How long do you have to fast?

The amount of time you will need to fast depends on the type of blood test you require. A tip to keep in mind: schedule your blood test for as early in the morning as you can. The hours you spend asleep are considered part of your fasting time. This can help make fasting easier.

• Glucose test: Typically, your doctor will ask you to fast for 8–10 hours before the blood test.
• Lipid tests: For blood tests to check your cholesterol, you may need to fast for 9–12 hours before the test.
• Iron tests: For tests to check your iron levels, you may need to fast for 12 hours before the tests.

Q:

What happens if you do not fast before a blood test?

Anonymous

A:

If you eat or drink something before lab work, and you were asked to fast before the labs, the results may be inaccurate. For example, if you eat before having a “fasting glucose test,” your glucose level may come back falsely elevated, leading to an inaccurate diagnosis.

Lauren Castiello, M.S., AGNP-C Answers represent the opinions of our medical experts. All content is strictly informational and should not be considered medical advice.

Can you drink coffee before a blood test?

Typically, you cannot drink coffee before a fasting blood test. This is because coffee contains caffeine, which absorbs into your bloodstream. As such, it can skew the results of your blood test.

Coffee is also a mild diuretic. This means that it helps your body get rid of water and salt by causing more frequent urination. This can have a dehydrating effect. In turn, this can make it more difficult for the technician to draw your blood.

Read more about caffeine.

Can you drink alcohol before a blood test?

It is generally a good idea to avoid drinking alcohol when fasting before a blood test. Alcohol can cause irregularities in:

• enzymes
• blood sugar
• fat levels

This can affect the results of your blood test. If you have any doubts about what you can or can’t drink, speak with your doctor or simply leave it out before a blood test.

Can you drink water before a blood test?

Typically, water is the one thing you can have while fasting for a blood test. Drinking water can actually be useful before your test.

Drinking water before a blood test can help hydrate and plump up your veins. This can make it easier for the technician to find your veins and draw your blood. Water can also help keep your blood pressure from dropping during the blood draw.

How can you prepare your child to fast before a blood test?

It can be difficult when your child requires any kind of test, including a blood test. However, there are ways you can help prepare yourself and your child ahead of time.

Ways to prepare your child for a blood test include:

• Explain things to them in advance.
• Stay positive, as you may feel more anxious than your child. Try to stay upbeat to keep them calm.
• Bring a distraction, such as their favorite toy.
• Ensure they are well hydrated before their blood draw.
• Let them look if they want to. Your instinct may be to cover their eyes, but this can increase their anxiety.
• Lend a hand. You may be asked to hold your child to provide comfort and help them stay secure.
• Bring a snack. If they are fasting, your child might be grateful to have a snack ready when the blood draw is complete.

Other frequently asked questions

These are some more questions people asked about fasting for a blood test. They have been reviewed by Lauren Castiello, M.S., AGNP-C.

What should you not do before a blood test?

Before a fasting blood test, you should not eat or drink anything other than water. Your doctor will tell you how long you should fast before the test. You also should not do the following before your blood test:

• chew gum
• smoke
• exercise

Can you take medications before a blood test?

It’s important to ensure your doctor knows about any medications, vitamins, and supplements you take before your blood test. Generally, it’s fine for you to continue taking your medication as you usually would. However, speak with your doctor and follow any instructions they give you.

Summary

Many blood tests can be done without fasting. However, some require you to fast beforehand, including glucose, cholesterol, and iron tests.

Your doctor will tell you how long you need to fast before your blood test. Typically, this will range from 8–12 hours. During this time, you should not eat or drink anything other than water unless otherwise instructed by your doctor. Follow the guidance from your doctor on whether or not to take medications before your test.

Drinking water before your blood test can help hydrate and plump your veins. This can make for a smoother blood draw. You can also schedule your test for as early in the morning as possible, so much of your fasting time will be when you are asleep.

What are the rules for fasting for blood work?

Is 7 hours of fasting enough for blood test?

Can you drink water before a fasting blood test?

Can I drink coffee while fasting for blood work?