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. The United States has 11,792 practicing hematologists. Broken out by state, hematology doctor density in Alabama is 141, in Alaska is 15, in Arizona is 163, in Arkansas is 92, in California is 1,264, in Colorado is 174, in Connecticut is 203, in Delaware is 25, in District of Columbia is 109, in Florida is 715, in Georgia is 285, in Hawaii is 39, in Idaho is 30, in Illinois is 557, in Indiana is 244, in Iowa is 108, in Kansas is 88, in Kentucky is 148, in Louisiana is 147, in Maine is 71, in Maryland is 273, in Massachusetts is 560, in Michigan is 355, in Minnesota is 281, in Mississippi is 86, in Missouri is 226, in Montana is 35, in Nebraska is 85, in Nevada is 79, in New Hampshire is 59, in New Jersey is 375, in New Mexico is 69, in New York is 1,078, in North Carolina is 385, in North Dakota is 32, in Ohio is 462, in Oklahoma is 94, in Oregon is 144, in Pennsylvania is 648, in Rhode Island is 69, in South Carolina is 140, in South Dakota is 26, in Tennessee is 235, in Texas is 712, in Utah is 96, in Vermont is 28, in Virginia is 247, in Washington is 272, in West Virginia is 75, in Wisconsin is 226, and in Wyoming is 17.