A high white blood cell count typically indicates a bacterial or viral infection; a disorder of the immune system; a reaction to medication; leukemia; allergic reaction; stress; or smoking, as stated by Mayo Clinic. Tuberculosis and rheumatoid arthritis are also common causes of an increase in white blood cells.
White blood cells are disease-fighting cells. A high count is the body's natural reaction to combat illness. A count that exceeds 11,000 leukocytes in a micro liter of blood is considered high for adults, according to Mayo Clinic. Normal white blood cell levels for children varies according to age and weight.