What is the complete blood count test?

The complete blood count is the calculation of the cellular (formed elements) of blood. These calculations are generally determined by specially designed machines that analyze the different components of blood in less than a minute.

A major portion of the complete blood count is the measure of the concentration of white blood cells, red blood cells, and platelets in the blood. The complete blood count (also called CBC) is generated by testing a simple blood sample.

What are values for a complete blood count?

• White blood cell count (WBC). The number of white blood cells in a volume of blood. Normal range varies slightly between laboratories but is generally between 4,300 and 10,800 cells per cubic millimeter (cmm). This can also be referred to as the leukocyte count and can be expressed in international units as 4.3 - 10.8 x 10⁹ cells per liter.
  
   
• White cell differential. A machine generated percentage of the different types of white blood cells, usually split into granulocytes, lymphocytes, monocytes, eosinophils, and basophils.
  
   
• Red cell count (RBC). The number of red blood cells in a volume of blood. can be expressed in international units as 4.2 - 5.9 x 10¹² cells per liter.
  
   
• Hemoglobin (Hb). The amount of hemoglobin in a volume of blood. Hemoglobin is the protein molecule within red blood cells that carries oxygen and gives blood its red color.
  
   
• Hematocrit (Hct). The ratio of the volume of red cells to the volume of whole blood.
   
• Platelet count. The number of platelets in a volume blood. Platelets are not complete cells, but actually fragments of cytoplasm from a cell found in the bone marrow called a megakaryocyte. Platelets play a vital role in blood clotting.

Electrolytes

Electrolytes are substances that become ions in solution and acquire the ability to conduct electricity. The balance of the electrolytes in our bodies is essential for normal function of our cells and our organs.

Common electrolytes that are measured by doctors with blood testing include sodium, potassium, chloride, and bicarbonate.

Sodium: Sodium regulates the total amount of water in the body and the transmission of sodium into and out of individual cells also plays a role in critical body functions. Many processes in the body, especially in the brain, nervous system, and muscles, require electrical signals for communication. The movement of sodium is critical in generation of these electrical signals. Too much or too little sodium therefore can cause cells to malfunction, and extremes (too much or too little) can be fatal.

Potassium:  The proper level of potassium is essential for normal cell function. Among the many functions of potassium in the body are regulation of the heartbeat and function of the muscles. A seriously abnormal increase of potassium (hyperkalemia) or decrease of potassium (hypokalemia) can profoundly affect the nervous system and increases the chance of irregular heartbeats (arrhythmias), which, when extreme, can be fatal.

Chloride:  Chloride also plays a role in helping the body maintain a normal balance of fluids.