Some blood tests, such as the tests to measure total cholesterol or blood glucose levels, require you to fast for a set amount of time before the test. Your doctor may ask you to fast anywhere from two to 12 hours before your test. Having foods digesting in your system can affect the results of the test.
Liquids
It is permissible to drink water. In fact, it is important to drink water if you are fasting because you do not want to get dehydrated. Do not add lemon or any flavorings to your water, though. Drink it plain. Avoid other beverages, such as juice, coffee or soft drinks.
Food
Avoid all food during the recommended fasting time. For this reason, doctors usually schedule blood tests that require fasting for early in the morning so that you can stop eating after dinner and avoid food until your test. (If you work a night shift or other non-standard hours, ask your doctor to schedule your test for close to your normal wake-up time.) Do not chew gum, eat breath mints or consume other food substitutes during the fast time.
Medication
Some medications may affect test results. Make sure your doctor is aware of any medications you are currently taking. Follow his directions for maintaining or changing your medication schedule prior to your blood test. Do not stop taking your regular medications unless your doctor tells you to do so.
Herbs, Vitamins and Supplements
Certain herbs, vitamins and supplements can affect blood test results. Let your doctor know about any products you use regularly and follow his advice about taking them or avoiding them during your fasting period. If you have not checked with your doctor, postpone taking your herb, vitamin or supplement until after your blood test to be sure it does not interfere with your results.
