why do you have to fast for blood tests


It\’s the morning of your bloodwork and your doctor said to fast before the test. But your
is growling and you have serious withdrawal hours before you roll up your sleeve. A bite of toast and a few gulps of won\’t really make a difference, right? Not so fast. Your results could come back wrong if you give in to temptation. Fasting means you don\’t eat or drink anything but usually for 8 to 12 hours beforehand. So, if your appointment is at 8 a. m. and you\’re told to fast for 8 hours, only is okay after midnight. If it\’s a 12-hour fast, avoid food and drink after 8 p. m. the night before. You also shouldn\’t smoke, chew gum (even sugarless), or. These things can rev up your digestion, and that can affect your results. Take your prescription unless your doctor tells you to skip them. But ask your doctor before you take any over-the-counter drugs.

What Tests Do I Fast For? tests help doctors check for certain health problems and find out how well your body is working. Doctors also use them to figure out how well treatments are working. You don\’t need to fast before all tests. Your doctor will tell you if you need to. Fasting blood glucose measures the amount of glucose ( ) in your blood to test for or. Lipid profile is used to check the level of and other blood fats. High levels put you at risk for developing or having a. Basic or comprehensive metabolic panel is often part of a routine physical. The tests, electrolyte and fluid balance, and function. The comprehensive test checks your, too. Renal function panel is used to gauge the health of your and how well they\’re working. Vitamin B12 test measures how much of the vitamin is in your blood.

It can help diagnosis a specific type of and other problems. Some medications can interfere with this test. Tell your doctor about all the drugs you take. Iron tests are used to see if iron levels in your system are too low or too high. Gamma-glutamyl transferase (GGT) shows the level of the GGT enzyme in your system. A high reading may indicate disease, bile duct problems, or. Your doctor may ask you to fast for at least 8 hours beforehand. You also may need to avoid and some prescription drugs the day before the test because they can affect GGT levels. Talk to your doctor before stopping any prescribed medicines. Some blood tests will require you to fast beforehand. In these cases, your doctor will instruct you not to eat or drink anything, except water, in the hours leading up to the test.

Fasting before certain blood tests is important to help make sure that your test results are accurate. The vitamins, minerals, fats, carbohydrates, and proteins that make up all food and beverages can impact blood-level readings, clouding the results of your test. Not all blood tests will require you to fast beforehand. Blood tests that you will likely need to fast for include: If your doctor has prescribed a new blood test for you, or doesnвt mention whether or not you should fast or for how long, ask them if fasting is required. Some tests, such as a fecal occult blood test, donвt require fasting but do limit certain foods. Red meats, broccoli, and even some medications may cause a false positive test. Always follow your doctorвs advice when preparing for a test.

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