White blood cell (WBC) count is monitored routinely as part of a complete blood count. It is sometimes monitored by itself to monitor recovery from illness. Certain conditions and medications weaken the immune system and cause a decrease in white blood cells, while infections and disease can cause very high numbers of white blood cells. The WBC count detects dangerously low and high numbers of these cells.
White blood cells, or leukocytes, are cells of the immune system that work to defend the body against infections and other foreign matter. Most WBCs are made in the bone marrow and are found in blood and lymph tissue. There are five major types of WBCs: neutrophils, lymphocytes, monocytes, eosinophils and basophils. Disorders of the WBCs may involve only one of the five types, or it may involve two or more types together.
Normal White Blood Cell Count
Usually people produce about 100 billion white blood cells a day. The number of WBCs is expressed as cells per microliter of blood. A normal WBC count is usually between 4,000 and 11,000 cells per microliter of blood. A clinically significantly decreased WBC count is known as leukopenia.
White Blood Cell Considerations
White blood cell count tends to be lower in the morning and higher in the afternoon. Infants tend to have a higher WBC count than adults. Many medications can cause either an increase or decrease in WBC count. Low WBC is usually defined as lower than 3,500 white blood cells per microliter of blood.
Most Common Causes
Low WBC can have a variety of causes. Possible causes include viral infections, congenital disorders, autoimmune disorders and drugs such as prednisone, antibiotics and diuretics. Severe allergic reactions, parasitic diseases and vitamin deficiencies are other examples of causes of low WBC count. White blood cell counts can drop as the result of chemotherapy, radiation or certain types of cancer. Low WBC count can also indicate diseases of the liver or spleen or collagen-vascular diseases such as lupus erythematosus.
Having a low WBC can be dangerous. White blood cells are the body's defence mechanism against infections. If you have too few WBCs, you are at risk for all types of infections, including bacterial, viral and fungal. A WBC count lower than 2,500 cells per microliter of blood is considered dangerously low. Treatment of low WBC depends on identifying the cause.