Hematology is the study of the blood and blood disorders in the body. A hematologist is a physician who has expertise in diseases of the blood and bone marrow, and treats vascular and clotting problems. The hematologist also treats blood disorders such as hemophilia, leukemia, lymphoma, anemia and sickle cell disease.

Physicians in this specialty treat patients suffering from numerous diseases and illnesses, but some of the most common are malaria, lymphoma, non-hodgkin's lymphoma, myelomas, evans' syndrome, aids, leukemia, hemophilia, thrombocytopenia, sickle-cell disease, myeloma, pernicious anemia, hodgkin's disease, thalassemia, myelofibrosis, infectious mononucleosis, agranulocytosis, systemic lupus erythematosus (sle), megaloblastic anemia, and autoimmune hemolytic anemia.

Once properly diagnosed, practitioners can perform numerous procedures on patients including chemotherapy, bone marrow transplant, blood transfusion, radiotherapy, intramuscular injections, anticoagulation therapy, and venesection.

To diagnose patients with possible illnesses and diseases, specialists will often perform one of many tests including coombs test, d-dimer, prothrombin time, bone marrow biopsy, protein electrophoresis, serum ferritin level, partial thromboplastin time, vitamin b12 and folate levels, erythrocyte sedimentation rate (esr), blood film, full blood count, and hemoglobin electrophoresis.

Doctor density varies by specialty and location. Washington, D.C. has 68 practicing hematologist in Washington.

According to 2005 Census estimates, Washington, D.C. has a population of 550,521. Of this population, 110,240 are under the age of 18 and 66,591 are at or above the age of 65.