Do You Really Need to Fast Before a Blood Test?

Laboratory testing, including getting blood tests, is an integral part of maintaining your overall health. To get the most accurate result possible, many blood tests require you to fast beforehand.

At Nguyen Medical Group in Boynton Beach, Florida, primary care physician Thomas Nguyen, MD, guides you through everything needed to get ready for a successful blood test. Learn why fasting can be necessary for a blood test and how to prepare.

Why you might need a blood test

Blood testing is an essential preventive health care tool, as well as a way to monitor certain chronic conditions. Our team often orders blood tests at your annual physical or as part of a chronic disease management plan.

Conditions we can check for or manage with blood tests include:

• Diabetes
• High cholesterol
• Anemia 
• Some cancers
• Pregnancy

Blood tests can also help us determine your metabolic processing rate, electrolyte levels, and counts of blood cells and platelets.

Why is fasting important for blood tests?

Some blood tests require you to fast beforehand to get an accurate result. Eating and drinking require your bloodstream to work to absorb the various nutrients you have ingested.

When your body is working hard to absorb your food, many of the metrics measured during a blood test change. We aren’t able to get an accurate reading of these with food in your system.

Getting a blood test after fasting allows for the most precise assessment, enabling us to monitor and treat you effectively. 

How to fast for your blood test

Our team lets you know ahead of time what blood tests you need and whether you need to fast for them. Most tests that require fasting have an 8-12 hour window where you can’t eat or drink. Sometimes you need to avoid alcohol for a longer period.

Usually, we recommend scheduling the fasting blood tests first thing in the morning. That way, you can spend most of your fasting time asleep.

If you have a medical condition, such as diabetes, that makes fasting more challenging, need to stop taking medication temporarily, or are pregnant, our team provides you with additional care advice to keep your fast safe.

During the fasting period

Fasting includes avoiding all food and drinks, except still water. This includes the following items:

• Chewing gum
• Certain medications
• Smoking
• Coffee and sparkling water

We encourage you to continue drinking plain water to stay hydrated.

Let our team know if anything comes up or if you accidentally break your fast. We might need to reschedule for another time and have you repeat the fast.

After the fast

You can eat and drink immediately after your blood test is complete. You can even bring a snack to the office to eat right after the test.

We recommend eating a healthy meal shortly after the blood test. You can return to your usual activities immediately. 

Although fasting can be mildly uncomfortable, the benefits you get from a fasting blood test are worth it for your health. Contact us to schedule your medical testing or any other preventive care needs.