Fasting Diet Before Bloodwork

June 28, 2011

28 Jun – It may seem simple to follow a fasting diet before a blood test, but your lifestyle and eating habits can get in the way of a successful trip to the lab. Any deviation from your doctor’s instructions may postpone the prescribed test, its potential results and any medical treatment you might need.  Knowing when and why to fast will help you commit to and follow through with the brief period of fasting necessary to the correct outcome of your blood test.

Common Fasting Blood Tests

Your doctor may request a laboratory test to establish your level of health and relative risk for certain medical conditions. Tests that might require preparatory fasting include examinations of your blood glucose, cholesterol and triglyceride levels. These may be part of a group of tests called basic metabolic panels or lipoprotein panels. A blood sample drawn for one nonfasting test, such as a complete blood count, may require fasting if it will be used for additional assessments.

Fasting Rationale

Your doctor may want to compare your body chemistry with and/or without outside influences such as food or drink. The technician may establish a baseline and followup assessment of your blood content in the presence or absence of your normal diet. Anything that you ingest that remains in your body up until the test can influence your blood work and may inhibit your doctor’s ability to determine your health condition. Water intake, however, is necessary during the fasting period to maintain the fluid-electrolyte balance between your body tissues and blood volume.

What To Do Before Your Test

Your health care provider will give you instructions for exactly when and how long to fast, depending on when your test is scheduled. Eight to 12 hours of fasting is the norm.  This means that you should eat a normal meal prior to kick-off time for your fast, to provide ample blood sugar for healthy body function until after your blood is drawn. Then, during the fast period, drink only water. Start and stop fasting as recommended, fasting no longer than 14 hours in order to recover fully from your blood draw.

What Not To Do Before Your Test

Some medications may affect blood testing, so follow any of your doctor’s instructions on avoiding or delaying doses beforehand. Don’t drink coffee, tea, diet soda, juice, energy drinks or anything other than water while fasting. Don’t eat candy or other snacks or meals. Don’t smoke, chew gum or dissolve mints in your mouth.

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