Can you drink water while fasting for a blood test?

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Can you drink water while fasting for a blood test?
(Image by, courtesy of Kyle May)

You should not have anything to drink or eat prior to a fasting blood test. Small amounts of water, however, are allowed, according to St. Michael's Hospital in Toronto.

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Types of blood tests that may require fasting include fasting glucose, fasting lipids, fasting triglycerides and glucose tolerance.


The function of fasting blood tests is usually to determine the normal range of sugar in your bloodstream, which is why it is important not to consume anything that might affect this result.


A fasting blood test is commonly used to diagnose diabetes or to monitor blood sugar levels in diabetics, according to Blue Cross and Blue Shield Diabetes Center in Rhode Island.

Time Frame

You should refrain from eating or drinking anything, other than small amounts of water for 12 hours prior to a fasting blood test, according to St. Michael's.


Although water will probably not effect your glucose levels, drinking too much water can cause other measurements, such as sodium, to be too low, according to Dr. Mercola, a prominent physician who advocates blood tests to determine imbalances in the blood.

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