Venipuncture is the collection of blood from a vein. It is most often done for laboratory testing.
Most of the time, blood is drawn from a vein located on the inside of the elbow or the back of the hand.
In infants or young children, a sharp tool called a lancet may be used to puncture the skin and make it bleed. The blood collects onto a slide or test strip. A bandage may be placed over the area if there is any bleeding.
The steps you need to take before the test will depend on the kind of blood test you are having. Many tests do not require special steps.
In some cases, your health care provider will tell you if you need to stop taking any medicines before you have this test or if you need to be fasting. Do not stop or change your medicines without talking to your provider first.
You may feel slight pain or a sting when the needle is inserted. You may also feel some throbbing at the site after the blood is drawn.
Blood is made up of two parts:
Plasma is the fluid part that contains substances such as glucose, electrolytes, proteins, and water. Serum is the fluid part that remains after the blood is allowed to clot in a test tube.
Cells in the blood include red blood cells, white blood cells, and platelets.
Blood helps move oxygen, nutrients, waste products, and other materials through the body. It helps control body temperature, fluid balance, and the body's acid-base balance.
Tests on blood or parts of blood may give your provider important clues about your health.
Normal results vary with the specific test.
Abnormal results vary with the specific test.
Reviewed By: Laura J. Martin, MD, MPH, ABIM Board Certified in Internal Medicine and Hospice and Palliative Medicine, Atlanta, GA. Also reviewed by David Zieve, MD, MHA, Medical Director, Brenda Conaway, Editorial Director, and the A.D.A.M. Editorial team.