Could be infection. A high band count usually refers to how many white blood cells are actively maturing. When the band count is high, it usually refers to an escalating infection, or due to some other major stress. Talk to your doctor to find out why. Uncontrolled infections can be life-threatening.
Increased production. When the bone marrow accelerates the production of white blood cells, usually in response to an infection, slightly immature white blood cells are released into circulation. Bands are slightly immature white blood cells. By itself, high band count does not need treatment, the cause of high band count needs to be ascertained and treated.