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 substance alanine aminotransferase, or ALT, appears in a blood test in higher amounts when the liver is damaged, according to WebMD. Low levels of ALT are normally found in the bloodstream even with a perfectly functioning liver.Full Answer >
The BMP, or basic metabolic panel, blood test is performed to test the body's blood acid and base balance, blood sugar levels and kidney function, according to MedlinePlus. The basic metabolic panel checks CO2 levels, BUN level, creatinine, glucose, serum chloride, serum sodium and serum potassium, notes MedlinePlus.Full Answer >
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 >
As a general rule, patients should avoid eating or drinking anything other than water during the 12 hours prior to any blood test. Blood tests specifically prohibiting alcohol consumption in the 24 hours prior to the administration include the triglyceride test and the gamma glutamyl transferase (GGT) test.Full Answer >