Hematopathology is the study of diseases of blood cells (White blood cells, red blood cells, platelets) and cells/tissues/organs comprising the hematopoietic system. The term hematopoietic system refers to tissues and organs that produce and/or primarily host hematopoietic cells and include bone marrow, lymph node, thymus, spleen, and other lymphoid tissues. In the United States, hematopathology is a board certified subspecialty (American Board of Pathology) practiced by those physicians who have completed general pathology residency (anatomic, clinical, or combined) and an additional year of fellowship training in hematology. The hematopathologist reviews biopsies of lymph nodes, bone marrows and other tissues involved by an infiltrate of cells of the hematopoietic system. In addition, the hematopathologist may be in charge of flow cytometric and/or molecular hematopathology studies. After the hematopathologist makes the diagnosis, the hematologist or hemato-oncologist can make a decision about the best course of action.