Elevated levels of leukocytes, or white blood cells, may indicate a problem with the patient's immune system, a reaction to a drug or an infection, according to Mayo Clinic. Even smoking can raise white blood cell levels.
High white blood cell levels are also a symptom of different types of leukemia, including chronic and acute lymphocytic and myelogenous leukemia, according to Mayo Clinic. A high count can also be a symptom of a bacterial or viral infection, rheumatoid arthritis, whooping cough and tuberculosis. Myelofibrosis also causes elevated leukocytes. Myelofibrosis is a type of leukemia that interferes with the bone marrow's production of blood cells.