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What You Need To Know About Fasting, Before Your Lab Test

In preparation for your lab visit, you may be asked to follow a specific set of instructions which may include fasting (stop eating or drinking anything except for water for a period of time). With certain blood tests, you may be instructed to fast for up to 12 hours before your lab test.You do not have to fast unless your healthcare provider has ordered a test that requires fasting. Generally, two common tests that are done while fasting are the glucose and lipid panel tests. Be sure to ask your provider if fasting is required for your test prior to having your test completed. Consuming food and beverages prior to a lab test could affect your test results. Fasting helps to ensure we obtain the most accurate results possible by limiting the impact of added factors during testing.

Fasting does not exclude the consumption of water. It is important to prepare your veins by drinking enough water to keep them hydrated. The more hydrated you are, the more helpful it will be for the lab technician to find them. Drink plenty of water before having any blood test performed.

Fasting for a lab test typically lasts 8 to 12 hours. Your provider should give you any special instructions related to your tests, including fasting requirements, recommended water intake and/or certain medications to avoid. If you think fasting might be a problem, consult your healthcare provider with your concerns.

Once you’ve had your lab test, you can eat and drink something immediately.

For your convenience, Memorial Hermann Diagnostic Laboratory locations are walk-in labs -- no appointment is necessary. Wait times will vary depending upon the number of patients, and are typically longer in the mornings.

Find a Memorial Hermann Diagnostic Laboratory location near you.