Why should you fast before blood tests?

Answer

Fasting for a certain length of time before a blood test is one way of ensuring that your test results are not contaminated by the food you've eaten. The Mayo Clinic notes that fasting may not be necessary to get an accurate reading on a cholesterol test, but most doctors will still ask that you fast for at least 12 hours before your appointment.

For certain other kinds of tests, such as a blood glucose test, fasting is necessary. This test is done to check for diabetes, and it requires that you abstain from any food intake for at least eight hours before the blood is drawn. There are alternatives to this test for diagnosing diabetes, but according to howstuffworks.com, the blood glucose test is easy, fast, and inexpensive.

Other types of blood tests do not require that you fast prior to the blood draw. The test for thyroid hormone in the blood, for example, almost never requires that you fast. But even here, there's an exception. About.com recommends fasting before a thyroid test if you are taking a time-released T3 medication such as Cytomel. In this case, your doctor might ask you to fast before your blood is drawn.

Q&A Related to "Why should you fast before blood tests?"
1. Calculate the time the fast begins. If the test is at 6 a.m. and you have to fast for six hours, stop eating at midnight. 2. Stop eating at the start time of your fast. This means
http://www.ehow.com/how_5133399_fast-before-blood-...
Usuallly it's a good 8 to 12 hours. With nothing to eat or drink for that time. If you take medications daily for health reasons, you may check with your doctor to see which are okay
http://wiki.answers.com/Q/How_many_hours_fasting_b...
Eight hours or more of fasting is enough for a fasting
http://www.chacha.com/question/how-long-are-you-su...
People taking Lithium need to have their blood tested periodically because Lithium, like most drugs, is poisonous at certain blood levels. The reason you need blood tests with Lithium
http://www.quora.com/Prescription-Medication/Why-d...
1 Additional Answer
Ask.com Answer for: Fasting before Blood Tests
How long to fast, if at all, before a blood test depends on what your blood will be tested for. For example, cholesterol, glucose, and glycohemoglobin blood tests require that you fast for 12 hours.
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