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Complete Blood Count
(CBC)

What Is a Complete Blood Count (CBC) Test?

The complete blood count (CBC) is one of the most commonly ordered blood tests. To understand this test, it is important to know that blood consists of two major parts: plasma and cellular elements. The plasma is the part of the blood that is liquid which allows the blood to flow easily. The other part of the blood consists of blood cells.

The major cells in the blood are white blood cells (WBC), red blood cells (RBC), and platelets. Each of these types of cells carries out specific and important functions.

The complete blood count test measures the quantity of all the different types of cells in the blood. It also provides some valuable information on other parameters related to each type of blood cell.

Complete Blood Count Procedure

Patient Comments

The complete blood count may be done in many different health care settings including doctors' offices, clinics, urgent care facilities, emergency rooms, hospitals, and outpatient medical laboratories.

The complete blood count test is performed by drawing a few milliliters (one to two teaspoons) of blood from a vein. Most commonly, the sample is obtained from a vein that is visible from the skin, such as a vein on the back of the hand or the inner angle of the elbow (antecubital fossa).

A tourniquet is usually applied to the area proximal to the vein (closer to the center of the body than the vein itself). This technique will make the vein more visible and plump by limiting the blood from the vein going back toward the heart. The tourniquet is only applied for a brief period of time (a few minutes at the most) and it is removed as soon as blood is drawn.

The skin overlying the vein is cleaned using an alcohol pad, and then a needle is inserted through the area of cleansed skin into the vein below where the tourniquet is applied. The blood is then pulled from the vein via the needle by gently pulling the plunger on the syringe or by a connection of the needle to a special vacuum vial that collects the blood.

This sample is then taken to the laboratory for analysis, and the complete blood count results may be available within hours after collection. Prompt delivery of the blood sample to the laboratory for analysis is important. A sample that is not delivered in a timely manner may yield inaccurate results.

Medically Reviewed by a Doctor on 10/24/2016

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