During a complete physical test, your doctor will order a Complete Blood Count (CBC) test to evaluate: 
- Red Blood Cell (RBC) count,
- White Blood Cell (WBC) count,
- The platelet count,
- Hemoglobin and haematocrit
- Mean red cell volume.
A complete blood count is usually ordered to help evaluate :
- The blood
- The bone marrow
- Oxygen-carrying capacity of the blood
- To identify infections
- Look for anemia and leukemia and
- Monitor the effects of chemotherapy and radiation therapy.
White blood cells, also known as leukocytes, play an important role in the immune system of an individual .
They fight infections in a process known as ‘phagocytosis’ where they surround the foreign organisms and destroy them. White blood cells also help in the production, transportation, and distribution of antibodies in order to build the body’s immune system. When an acute infection occurs, the white blood cells produce colony-stimulating factor (CSF), which further stimulates the bone marrow to increase the production of white blood cells. This production can be doubled within a few hours.
However, too many white blood cells doesn't always mean a good thing. A high white blood cell count (also called leukocytosis) isn't a specific disease but could indicate an underlying problem. This is why a high white blood cell count always requires further medical evaluation.
A normal white blood cell count is between 4,500 and 10,000 cells per microliter:
- 5,000 to 10,000 for men and children
- 4,500 to 11,000 for women
In the absence of any disease, they form just about 1% by volume of the total blood in the body. There are five different types of white blood cells and each serves a different function in the body. They are the neutrophils, band neutrophils, lymphocytes, monocytes, eosinophils and the basophils.  In a normal person, the number of white blood cells ranges are :
- Neutrophils: 3150 to 6200 (55% to 70%)
- Band neutrophils 50 to 200 (0% to 3%)
- Lymphocytes: 1500 to 3000 (20% to 40%)
- Monocytes: 300 to 500 (2% to 8%)
- Eosinophils: 50 to 250 (1% to 4%)
- Basophils: 15 to 50 (0.5% to 1%)
per micro liter of blood.
For example, a high neutrophil count would indicate an infection, a cancer, or physical stress while a high lymphocytes count would indicate AIDS . High monocyte and eosinophil counts usually pinpoint bacterial infection.
A high white blood cell count could indicate:
- Tissue damage (from burns)
- Use of certain medications, such as corticosteroids, antibiotics or anti-seizure drugs
- Chronic bone marrow diseases such as a myeloproliferative disorder
- Acute or chronic leukemia
- Diverticular Disease
- Intense exercise
- Severe physical or emotional stress .
High white blood cell counts are considered normal in certain situations:
- Pregnancy in the final month and labor may be associated with increased WBC levels.
- Spleen removal could grant persistent mild to moderate increased WBC count.
- Healthy newborns and infants a have higher WBC counts than adults.
- Too much smoking could also cause an increased WBC count.
The WBC count tends to be lower in the morning and higher in the late afternoon and they are age-related.
However, when the white blood cell counts continue to rise or fall to abnormal levels it means that the condition is getting worse — scientists are still not certain if besides being a good indicator of a problem, high white blood cell counts could also trigger a serious disease if they naturally rise after an illness.
An elevated white blood cell count always signifies your immune system is working harder than usual. This could happen simply because your body is preparing for pregnancy, or it could be your body’s response to a seasonal allergy, cold or flu, or even strenuous exercise and emotional stress.
Your body is a very complex machine and when something is out of the ordinary it responds with something as simple as elevating white blood cell count. In very simplified language, your body’s immune system signals white blood cells – I am under stress, I need you to protect me better. And white blood cells start multiplying.
One thing is certain though. You should not ignore your doctor's orders to have a white blood count done. It is a reliable and inexpensive way to enable better and faster diagnosis and prognosis.