Your doctor may ask you to take a fasting blood test to determine your cholesterol or blood sugar levels. The process of fasting ensures that the results of your blood test will not be confused by foods that you have eaten during the last few hours that your body has not fully absorbed. You should not eat food, drink coffee or take some medications for eight to 12 hours before a fasting blood test, but most physicians agree that you can drink water.
Effects of Water on Blood Test Results
Although eating food or consuming drinks containing nutrients, calories or sugar will affect the results of your fasting blood test, drinking water will have no measurable impact because it contains no calories, fats or sugars.
Dehydration and Drawing Blood
Fasting Blood Tests & Black Coffee
If you are dehydrated when the nurse or physician performs your fasting blood test, it can be difficult for them to draw blood from your veins. Drinking water makes your veins plump and easy to access. For this reason it as actually a good idea to drink water before your fasting blood test.
Dehydration and Triglycerides
Dehydration can also affect your triglyceride count, which is one part of the lipid panel that doctors test along with your cholesterol by means of a fasting lab. It is a good idea to drink water before your lipid panel fasting blood test in order to reduce the risk of a deceptively high triglyceride reading due to dehydration.
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Devra Gartenstein is an omnivore who has published several vegan cookbooks. She has owned and run small food businesses for 30 years.