Hematology is the study of blood and blood disorders. Hematologists and hematopathologists are highly trained healthcare providers who specialize in diseases of the blood and blood components. These include blood and bone marrow cells. Hematological tests can help diagnose anemia, infection, hemophilia, blood-clotting disorders, and leukemia. Bone marrow biopsy is not a common test in general, but is a common test for hematologists. It involves taking cells from the bone marrow for analysis for many types of disease.