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Venipuncture

Blood-draw; Phlebotomy

Venipuncture is the collection of blood from a vein. It is most often done for laboratory testing.

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Blood test

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How the Test is Performed

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.

How to Prepare for the Test

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 medications without talking to your provider first.

How the Test will Feel

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.

Why the Test is Performed

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 doctor important clues about your health.

Normal Results

Normal results vary with the specific test.

What Abnormal Results Mean

Abnormal results vary with the specific test.

Related Information

Fibrinogen blood test
Blood clots
Platelet count

References

Harbert KR. Venipuncture. In: Dehn RW, Asprey DP, eds. Essential Clinical Procedures. 3rd ed. Philadelphia, PA: Elsevier Saunders; 2013:chap 5.

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Review Date: 4/30/2015  

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, Isla Ogilvie, PhD, and the A.D.A.M. Editorial team.

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