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.Know More
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.Learn more about Diagnostics & Imaging
The easiest way to determine a person's blood type is to perform a blood test that checks for certain blood markers called antigens, according to WebMD. The test checks for two markers: ABO and Rh. The ABO test determines if the blood is type A, B, AB or O.Full Answer >
In a blood test, MCV represents the mean corpuscular volume, which is a measure of the average size of the red blood cells. The MCV is aÂ red blood index that is part of a complete blood count test.Â The bloodÂ test is performed to diagnose anemia.Full Answer >
Unless specifically requested by a doctor, fasting is typically not required prior to a prostate-specific antigen, or PSA, blood test, according to Lab Tests Online. If fasting is required, patients must consume no food or drinks, except water, for a time period prior to the lab test, explains Quest Diagnostics.Full Answer >
An international normalized ratio, or INR, blood test is one that is useful in determining how long it takes an individual's blood to clot. The test works by measuring the international normalized ratio and is generally ordered for people who take warfarin, which is a medication that thins the blood, according to Mayo Clinic.Full Answer >