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A high white blood cell count may be caused by a wide range of conditions, which include normal physiological responses to stress, allergic reactions, infection and serious conditions such as cancer. Treatment usually depends on the cause or disease.

Our blood contains solid particles in the form of red blood cells (RBCs), white blood cells (WBCs), and platelets as well as a liquid component called plasma. The red blood cells function mainly to transport oxygen to the various tissues and organs while the platelets work mainly to prevent or stop bleeding.  On the other hand, our white blood cells, which consist of five types of cells, have various functions, but mainly to protect the body from disease. The cells in the blood are manufactured primarily in the bone marrow and are released to the circulation upon maturation.

Getting a complete blood count (CBC) is part of a routine laboratory work-up. It may also be requested to help diagnose a medical problem. Occasionally, your doctor may find that you have a high white blood cell count, a condition also called leukocytosis. In most cases, the cause of the high white blood cell count is related to an on-going condition, such as an infection, but less frequently, it may be due to a serious disorder, such as leukemia. The values that doctors consider as a high WBC count may differ from one medical practice to another. Furthermore, the threshold for a high white blood cell count in kids varies with their age and size. In adults, a WBC count of more than 11,000 per microliter of blood is considered higher than normal.

What Causes High White Blood Cell Count?

In general, a high WBC count may indicate that:

  • You have an increased production of WBCs in the bone marrow
  • Your body is reacting to a drug that causes an increase in WBC production
  • You have a disease in the bone marrow that is causing an abnormally high production of WBCs
  • You have an immune system disorder that causes an increase in WBC production

Sometimes, a high WBC count may indicate that you are experiencing unusual stress, which may be due to various factors, including intense exercise or severe emotional stress.

Leukocytosis (white blood cell count high) may be due to a wide range of causes. There are five distinct components of white cells that may contribute to an increase in the total number of your WBCs. Leukocytosis may occur due to an increase in one or a combination of these cells:

  • Neutrophils
  • Lymphocytes   
  • Eosinophils
  • Monocytes
  • Basophils

Sometimes immature white blood cells (blasts) from the bone marrow are also found in the blood. The type of cells involved in leukocytosis, which are found under microscopic examination may help the clinician find out what is causing your condition


The neutrophils make up about 59 percent of your white blood cell population. An increase in your neutrophil count (neutrophilia) may be due to:

  • Infection, which is the most common cause, frequently due to bacteria
  • Inflammation, which may be related to various conditions such as inflammatory bowel disease, vasculitis , or rheumatoid arthritis
  • Malignancy (cancer), including leukemia (cancer of the blood)
  • Stress
  • Certain drugs, including lithium, heparin, carbamazepine, Phenobarbital, phenytoin, minocycline, and steroids
  • Certain genetic conditions such as familial cold urticaria, familial neutrophilia

It is noteworthy to mention that some bacterial infections, such as typhoid fever, do not cause neutrophilia. Other bacterial infections may cause a decrease in neutrophils (neutropenia) include Staphylococcus aureus, rickettsia, and Mycobacterium tuberculosis. Severe and chronic infections may also cause your neutrophil count to decrease because the demand is higher than the rate of production.

Continue reading after recommendations

  • Mayo Clinic. High white blood cell count.
  • Medscape. Leukocytosis.
  • AAFP. Leukocytosis: Basics of Clinical Assessment . courtesy of Thirteen Of Clubs by Flickr:
  • Photo courtesy of Pulmonary Pathology via Flickr: