White blood cells scavenge the circulatory system for bacteria, viruses and other foreign invaders, playing a very important role in the body's immune system. A high white blood cell count on its own does not necessarily cause any specific medical problems, but may be a warning sign for certain diseases. If you have high white blood cell levels, your doctor may perform additional tests to determine if this increase is the result of a more dangerous underlying condition.
Infection and Inflammation
Infection is one of the most likely causes of increased white blood cell levels, according to the Mayo Clinic. As bacteria and viruses multiply in the body, the bone marrow will produce more white blood cells to battle the infection. Infections can also cause inflammation, which can likewise lead to an increase in white cell levels. White cell numbers will typically return to normal soon after an infection subsides.
Chronic Obstructive Pulmonary Disease and Smoking
Inflammation of the lungs can increase white cell production. Lung inflammation is one of the key features of chronic obstructive pulmonary disease (COPD), which includes emphysema and chronic bronchitis. COPD is commonly caused by smoking, states the National Heart Lung and Blood Institute. As the lungs and airways become inflamed, they recruit white blood cells to sites of inflammation. This in turn causes further airway restriction, inflammation and white cell production.
Autoimmune Diseases
White blood cells also have a role in autoimmune diseases, in which the body's immune system wages war against itself, according to the Merck Manual. A number of autoimmune conditions such as arthritis, Graves disease, lupus and type 1 diabetes can be associated with an increase white blood cell levels.
Leukemia
The Mayo Clinic describes leukemia as a cancer of the white blood cell-producing cells of the bone marrow. Leukemia causes a large number of abnormal white cells to be produced. These white cells are typically not functionally active but can show up on a white cell test as a sign of leukemia.
Stress
Psychological or physical stress can cause a temporary increase in white blood cell levels, notes the American Academy of Family Physicians. This rise is due to an overproduction of white cells during the stressful period and typically subsides soon after the stress is relieved.
