Locations:
Search IconSearch
February 16, 2022/Living Healthy/Primary Care

What You Should Know About Fasting Before a Blood Test

A Q&A to prep for your fasting blood test

two hands holding a stopwatch and a cup of water

So, your healthcare provider has asked you to fast before your blood test. Fasting means not eating and drinking for a period of time. You often need to do this before bloodwork. This is because what you eat and drink ends up in your bloodstream and can skew your results.

Advertisement

Cleveland Clinic is a non-profit academic medical center. Advertising on our site helps support our mission. We do not endorse non-Cleveland Clinic products or services. Policy

But can you drink black coffee when fasting for bloodwork? How about taking your medications? Family medicine specialist Timothy Tramontana, MD, MS, answers your frequently asked questions.

Q: How long should you fast for a blood test?

A: Typically, you should fast before bloodwork anywhere between 10 and 12 hours. Usually, people choose to do blood tests first thing in the morning. This way, you can fast overnight, when you generally don’t eat anyway.

Types of fasted blood tests

Blood tests are a quick, effective way for doctors to check your health and to see if certain treatments are working. Blood tests you may need to fast for include:

Q: Can you drink water before a fasting blood test?

A: Yes. You can drink as much water as you want, but it should be plain. Avoid lemon-flavored and carbonated waters, as well as teas until after your test.

Q: Can you drink black coffee when fasting for bloodwork?

A: Don’t drink anything but water. Coffee contains caffeine. It’s also a diuretic, which removes water from your body. Many people think coffee counts toward your fluid requirements. However, it makes you urinate more, which can affect some of your lab results. So, get your blood test done, then get your cup of coffee!

Advertisement

Q: Can you take medication before a fasting blood test?

A: You can take over-the-counter and prescription medications unless your doctor advises you otherwise. On that note, it’s definitely a good idea to tell your doctor about all medications and supplements you’re taking to avoid something potentially skewing lab results.

There’s no indication that daily medications — such as blood thinners and blood pressure meds — will cause any problems with fasting bloodwork, so definitely continue taking them unless told otherwise. And if you have a headache, taking an ibuprofen or another over-the-counter pain reliever shouldn’t cause any issues.

Q: What if you forgot to fast or ate something by accident?

A: Let your doctor know so you don’t end up doing a test unnecessarily. If you’ve already gone for the test without fasting, and the results come back normal, then you’re most likely OK. But if results come back abnormal, that may mean you have to redo the bloodwork while fasting.

Q: What if you have more questions about your test?

A: Call or send a message to your primary care team. Someone should be able to field your questions so you can feel as prepared as possible.

Advertisement

Learn more about our editorial process.

Health Library
Fasting for Blood Work

Related Articles

Person mixing baking soda and apple cider vinegar to make a home remedy
June 24, 2025/Skin Care & Beauty
Skip These 5 Home Remedies for Toenail Fungus

Some things you find in your house have antifungal properties — but that doesn’t mean they’ll clear your toenail fungus

Toes with athlete's foot fungus, tinea pedis, on them
June 23, 2025/Primary Care
Don’t Bother Using Home Remedies on Your Athlete’s Foot

Home remedies are unlikely to cure your contagious foot fungus — and they might even make it worse

Ear being pierced with a piercing gun
June 16, 2025/Skin Care & Beauty
Ear Piercing 101: Healing, Hurting, Cleaning and More

Earlobe piercings heal quicker and are less painful than cartilage piercings — proper cleaning and care are important

A family seeing their family doctor
June 2, 2025/Primary Care
6 Reasons You Should Have a Primary Care Provider or Family Medicine Provider

Having a PCP means knowing where to go for a range of concerns — that’s a good thing for your lifelong health

Two hands full of supplement tablets, pills and capsules, with healthcare provider in background
May 14, 2025/Primary Care
Why Your Doctor Needs To Know What Supplements You’re Taking

Over-the-counter pills, powders, extracts and tinctures can interact with other medications and cause unexpected side effects

Hands tucking pant legs into socks
May 8, 2025/Infectious Disease
How To Protect Yourself Against Tick Bites

Twice daily tick checks, the right bug sprays and long pants can help you prevent tick-borne diseases

Person wrapping a bandage around the arm of another person
May 7, 2025/Primary Care
How To Clean a Wound at Home — and When To Seek Medical Care

First, assess the seriousness of the wound, and then apply light pressure to stop any bleeding

Woman wearing period panties for free-bleeding during menstrual cycle
April 24, 2025/Women's Health
Go With the Flow: What You Need To Know About Free Bleeding

If you wash regularly and change your underwear as needed, this can be a safe (and liberating) alternative to pads and tampons

Trending Topics

Person in bed sleeping on their side, covers off
Breathing Problems? Try These Sleep Positions

If you’re feeling short of breath, sleep can be tough — propping yourself up or sleeping on your side may help

A couple looking at skyline, with one person slightly behind the other, head bent down
What Is Anxious Attachment Style — and Do You Have It?

If you fear the unknown or find yourself needing reassurance often, you may identify with this attachment style

Glasses and bottle of yellow-colored prebiotic soda, with mint, lemon and ginger garnish
Are Prebiotic Sodas Good for You?

If you’re looking to boost your gut health, it’s better to get fiber from whole foods

Ad