Is it okay to drink water while fasting for a blood test?

Author: Eulalia Toy  |  Last update: Friday, December 5, 2025

What is fasting for a blood test? If your health care provider has 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. While you're fasting for a blood test, you also should not: Chew gum.

Can I drink any water before a fasting blood test?

Yes, you can drink water when fasting for blood work. Healthcare providers recommend drinking water while you're fasting for a couple of reasons: Hydration. Staying hydrated is important for overall health, especially before a blood test.

What happens if you accidentally drink water while fasting for blood test?

Water: It is important to keep drinking water when fasting to stay hydrated. Water does not affect the results of a blood test.

Can drinking water affect fasting blood sugar results?

Drinking water before a fasting blood sugar test can actually decrease blood sugar levels, or at least prevent levels from getting too high. Water allows more glucose to be flushed out of the blood. When you're dehydrated, it means your overall blood volume is lower than normal, but your sugars will be the same.

Can I drink water when fasting?

Whether you're practicing intermittent fasting or simply fasting overnight for a blood test, drinking water is allowed and encouraged. However, it's important to note that certain religious fasting practices may not permit drinking fluids while fasting.

Fasting for a Blood Test: Dos and Dont’s

What happens if I accidentally drink water when fasting?

The general rule is that accidental ingestion of food or drink does not invalidate the fast. This concept is based on the idea that for a fast to be broken, there has to be an intention to break it.

What can I drink while fasting for blood work?

Liquids – water only

It's important to drink lots of water when fasting to stay hydrated. Water doesn't affect the results of a blood test and is perfectly fine to drink when asked to fast.

How long should you not drink water before fasting blood sugar?

For a fasting blood glucose test, you can't eat anything for 8 to 12 hours before the test. You should drink only water. Drinking water before your blood test may make it easier to take your blood. There is no special preparation for a random blood glucose test.

How to quickly improve blood test results?

For Accurate Blood Test Results: Fast

Nutrients and ingredients in the food and beverages you eat and drink are absorbed into your bloodstream. This could impact factors measured by certain tests. Fasting improves the accuracy of those tests, Dr. Krajcik says.

Can I drink water before a fasting cholesterol test?

You're generally required to fast, consuming no food or liquids other than water, for nine to 12 hours before the test. Some cholesterol tests don't require fasting, so follow your doctor's instructions.

Can you have sips of water when fasting for blood work?

If your health care provider has 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. While you're fasting for a blood test, you also should not: Chew gum.

Can I brush my teeth before a fasting blood test?

It's generally acceptable to brush your teeth while fasting before blood work, as long as you avoid swallowing any toothpaste or mouthwash. However, it's advisable to use plain water for rinsing rather than toothpaste to minimize the risk of inadvertently consuming substances that could affect test results.

Does fasting blood test mean no water?

Fasting means that you eat and drink nothing except water for 8–16 hours before your blood test. Fasting for 12 hours is optimal. Many people find it more convenient to complete the fast overnight and present for blood collection in the morning after.

Does not drinking water affect blood test results?

To protect cell membranes, the body may increase the production of cholesterol in response to severe dehydration. Due to dehydration, there can be inaccurate blood test results, as suspected, as water accounts for approximately 60% of the adult human body weight.

What can throw off a cholesterol test?

There are several things that can affect your cholesterol test results, from alcohol consumption to pregnancy to simple human error. Knowing about these factors may prompt you to share important information with your provider that can help them better interpret your results.

What can cause abnormal blood test results?

Abnormal levels of red blood cells, hemoglobin, or hematocrit may be a sign of dehydration, anemia, heart disease, or too little iron in your body. A low white cell count may be a sign of an autoimmune disorder, bone marrow disorder, or cancer.

How much water should I drink before a blood test?

Thoroughly Hydrate Before Your Blood Test

Being well-hydrated makes it much easier for the clinician to find a vein that can easily be punctured, without having to try multiple times. Ideally, you should begin drinking at least 64 ounces of water 24 hours before getting your blood test.

What foods should I avoid the night before a blood test?

Before undergoing a blood test, it's important to avoid certain foods and drinks that could interfere with your results. High-fat meals, sugary drinks, and alcohol can distort your blood sugar levels and other vital measurements.

What happens if you drink water before a fasting blood sugar test?

Yes excess water intake may interfere with your test results.

Does drinking water interrupt fasting?

Technically speaking, eating or drinking any calories breaks a fast. That means it's generally considered OK to drink black, unsweetened coffee or tea, as well as water.

What drink at bedtime lowers blood sugar?

Chamomile tea

The nutritionist suggests that those with diabetes can take a cup of chamomile tea before going to bed. She says the tea has anti-inflammatory, astringent, and antioxidant properties, which can help optimise blood sugar levels.

What happens if you accidentally drink water while fasting?

If a fasting person eats or drinks during the day in Ramadan by mistake (because he forgot he was fasting), his fast is still valid and he does not have to make up that day or offer expiation.

Is water allowed during fasting for blood work?

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.

Can walking before a blood test affect the results?

Avoid strenuous exercise in the 24 hours before your blood collection. Once again, doing this can skew the blood results, specifically increasing urea, CK and sometimes making your kidney function look worse than it actually is.

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