Deficiency of absolute number of leukocytes, which may be granulocytes (neutrophils, eosinophils, basophils) or lymphocytes (T-cells, B-cells).  The majority of cases of<unk>  are actually neutropenia since neutrophils constitute the majority of leukocytes.  As the principal function of white cells is to combat infection, a decrease in the number of these cells can place patients at increased risk for infection.  In pancytopenia, the other cell types in the blood (red blood cells and platelets) are similarly affected.  Neutropenia is a decrease in the number of circulating neutrophil granulocytes, the most abundant white blood cells. The terms<unk>  and neutropenia may occasionally be used interchangeably, as the neutrophil count is the most important indicator of infection risk.  However, neutropenia is more properly considered a subset of<unk>  as a whole.  Low white cell counts are associated with chemotherapy, radiation therapy, leukemia (as malignant cells overwhelm the bone marrow), myelofibrosis and aplastic anemia (failure of white and red cell creation, along with poor platelet production).  In addition, many common medications can cause<unk> . Other causes of low white blood cell count include: Influenza, systemic lupus erythematosus, typhus, malaria, HIV, tuberculosis, dengue, Rickettsial infections, enlargement of the spleen, folate deficiencies and sepsis. Many other causes exist.<unk>  can be identified with a complete blood count.
Leukopenia
Pancytopenia
Lymphocytosis
Agranulocytosis
Lymphocytopenia
Leukocytosis
Febrile neutropenia
Thrombocytopenia