What are the differences between leukemia and leukopenia?

High vs. low. Leukemia is a malignancy of the white blood cells, sometimes leading to excessive amounts of these cells in circulation. Leukopenia is a deficiency or low WBC count. Sometimes leukemia can present or lead to low WBC counts, but often leukemia is associated with a high WBC count.
Big difference. Leukopenia means low white blood cell count. Leukemia means cancer of the blood cells. Hope this helps.