A high white blood cell count is an increase in disease-fighting cells in your blood.  The exact threshold for a high white blood cell count varies from one laboratory to another. In general, for adults a count of more than 11,000 white blood cells (leukocytes) in a microliter of blood is considered a high white blood cell count.

Causes
An increased production of white blood cells to fight an infection
A reaction to a drug that increases white blood cell production
A disease of bone marrow, causing abnormally high production of white blood cells
An immune system disorder that increases white blood cell production

Specific causes of a high white blood cell count include:
Acute lymphocytic leukemia
Acute myelogenous leukemia (AML)
Allergy, especially severe allergic reactions
Chronic lymphocytic leukemia
Chronic myelogenous leukemia
Drugs, such as corticosteroids and epinephrine
Infections, bacterial or viral
Myelofibrosis
Polycythemia vera
Rheumatoid Arthritis

Natural Ways to Boost WBC
Take zinc
You probably already know that zinc is helpful when you first feel the symptoms of a cold coming on. A known immune booster, zinc is linked with the production of white blood cells. Studies have shown that even a mild zinc deficiency can increase risk of infection. The American Cancer Society also notes that some studies have shown zinc levels in blood and/or inside white blood cells were often lower in patients with head and neck cancer or childhood leukemia. Consume more oysters, beef, lamb, wheat germ, and spinach.

Take folic acid
The body needs folic acid to make white blood cells. In fact, one of the side effects of excess intake of folic acid is an increase in WBCs. A deficiency of folic acid can also lead to anemia, which is a low level of red blood cells. So if you’re low on either, increasing intake of folic acid may help. Eat more spinach, beans, and citrus fruits.

Take selenium
The University of Maryland Medical Center states that selenium can help build up white blood cells. Some studies also indicate that selenium may help prevent some infections. Another study indicated that when the elderly take both zinc and selenium supplements, their immune systems responded better to the flu vaccine than those who took placebo.

Eat more yogurt
Some studies have shown that people taking probiotics had stronger immune systems than those who didn’t take them. The probiotics also seemed to boost the WBC. A study conducted by German researchers and published in the Clinical Nutrition recruited nearly 500 healthy adults aged 18 to 67. All were given supplements, but only half received probiotic supplements. Over three months, those given the probiotics suffered fewer colds. In addition, a subgroup of over 100 participants who had their blood count measured showed higher white blood cell counts, indicating a stronger immune system.