URL of this page: //medlineplus.gov/ency/presentations/100152.htm

Complete blood count - series—Procedure

Procedure

Overview

A CBC requires a small blood specimen. Blood is drawn from a vein, usually from the inside of the elbow or the back of the hand.

Preparation: The skin should be cleaned with alcohol or iodine before the test. The patient should be seated comfortably or reclining.

How the test will feel:

When the needle is inserted to draw blood, some people feel moderate pain, while others feel only a prick or stinging sensation. After the blood is drawn, there may be some throbbing.

Although the CBC test is very safe, any blood drawing has a slight risk of complication, including:

  • Oozing of blood from puncture site
  • Fainting or feeling lightheaded
  • Hematoma (blood accumulating under the skin)
  • Multiple punctures to locate veins
  • Infection (a slight risk any time the skin is broken)

Review Date 11/26/2014

Updated by: Yi-Bin Chen, MD, Leukemia/Bone Marrow Transplant Program, Massachusetts General Hospital, Boston, MA. Also reviewed by David Zieve, MD, MHA, Isla Ogilvie, PhD, and the A.D.A.M. Editorial team.

Related MedlinePlus Health Topics