There are four types of Leukemia:
Acute myeloid leukemia (AML) and acute lymphoblastic leukemia (ALL) 
In these diseases, the original acute leukemia cell goes on to form about a trillion more leukemia cells. These cells are described as nonfunctional because they do not work like normal cells. They also crowd out the normal cells in the marrow. This causes a decrease in the number of new normal cells made in the marrow. This further results in low red cell counts (anemia), low platelet counts (bleeding risk) and low neutrophil counts (infection risk).
Chronic myelogenous leukemia (CML)
In chronic myelogenous leukemia (CML), the leukemia cell that starts the disease makes blood cells (red cells, white cells and platelets) that function almost like normal cells. The number of red cells is usually less than normal, resulting in anemia. But many white cells and sometimes many platelets are still made.
Even though the white cells are nearly normal in how they work, their counts are high and continue to rise. This can cause serious problems if the patient does not get treatment. If untreated, the white cell count can rise so high that blood flow slows down and anemia becomes severe.
Chronic lymphocytic leukemia (CLL)
In chronic lymphocytic leukemia (CLL) the leukemia cell that starts the disease makes too many lymphocytes that do not function. These cells replace normal cells in the marrow and lymph nodes. They interfere with the work of normal lymphocytes, which weakens the patient’s immune response. The
high number of leukemia cells in the marrow may crowd out normal blood-forming cells and lead to a low red cell count (anemia). A very high number of leukemia cells building up in the marrow also can lead to low white cell (neutrophil) and platelet counts. 
Unlike the other three types of leukemia, some patients with CLL may have disease that does not progress for a long time. Some people with CLL have such slight changes that they remain in good health and do not need treatment for long periods of time. Most patients require treatment at the time of diagnosis or soon after