Leukopenia means a decreased number of white blood cells. "Leuko-" refers to white blood cells, and "-penia" means deficiency or decrease. Leukocytosis means an increased white blood cell count and is often associated with infection, inflammation, stress response, or hematologic disorders. Thrombocytopenia means a decreased platelet count, which can increase bleeding risk after venipuncture. Erythrocytosis means an increased red blood cell count. This terminology matters to phlebotomy because laboratory orders and patient conditions often use hematologic language. The phlebotomist does not diagnose these conditions, but understanding terms helps the technician anticipate safety concerns and specimen requirements. For example, thrombocytopenia may require longer pressure after collection, while leukopenia may be associated with immunocompromised status and strict infection-control awareness. A CBC is the common test used to evaluate red cells, white cells, hemoglobin, hematocrit, and platelets. Reference topics: Phlebotomy Fundamentals; medical terminology; hematology; CBC components; blood cell disorders.