Some blood tests may require special preparations, such as fasting or discontinuing specific medications. Your care provider will let you know which preparations to take. If you’re not told to fast, you should drink plenty of water and follow your regular diet.

Blood tests are usually a quick and common procedure. The area the blood will be drawn from — usually the arm, either near the elbow or the wrist — is usually wrapped tightly with a band to make the vein easier to see, and then the access area is cleaned with an antiseptic wipe. The skin is pierced with a needle attached to a collection tube, and blood flows from the vein and into the collection tube.

Once the appropriate amount of blood is collected, the needle is removed and a bandage is placed over the site. Some discomfort and bruising at the injection site may be experienced.

Laboratory workers analyze the blood, looking at specific blood factors. Blood test results could be available within minutes or take a few weeks to be ready. Your doctor will discuss the test results with you.

• When Celiac disease is present, your blood test results will show higher than normal levels of certain antibodies. These antibodies will be present because when the body misidentifies gluten as a threat.
• When an inflammatory bowel disease is present, a blood test will show an increased white blood cell count, which may indicate inflammation.
• A blood test can reveal if a person has a Helicobacter Pylori infection, which is an indicator of stomach ulcers and could put a person at greater risk of stomach cancer. Stomach cancer can also be determined by looking for anemia — a low amount of white blood cells — which can be found by a complete blood count (CBC) test.
• A blood test to determine food allergies will look for the presence of IgE antibodies, which are made when a food is misidentified as a threat by the immune system.