The hallmark of leukemia is often an increase in the number of white blood cells. It’s ironic that mass production of white blood cells--your body’s infection fighters--actually causes you harm. The problem is that the white blood cells made when you have leukemia may not function normally. When your body makes too many leukemic white blood cells, it doesn’t make enough normal ones to fight infection. This decrease in the strength of your immune system is called immunosuppression. A weaker immune system means you are at a greater risk of getting both common infections you encounter in everyday life as well as uncommon ones.
White blood cells go through a process of maturation called differentiation. When something goes wrong during that process, your bone marrow makes abnormal, immature, white blood cells called blasts. These white blood cells may be released into your bloodstream before they’re fully formed. The type of leukemia you have depends on the type of white blood cell and the stage of differentiation in which the defect occurs.
With leukemia, you may also have a decrease in the number of red blood cells and platelets, which get crowded out by the increase in white blood cells. This can lead to other health problems, such as feeling tired all of the time or having an increased risk of serious bleeding.