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 14,031 practicing hematologists. Broken out by state, hematology doctor density in Alabama is 166, in Alaska is 18, in Arizona is 200, in Arkansas is 116, in California is 1,468, in Colorado is 209, in Connecticut is 238, in Delaware is 31, in District of Columbia is 125, in Florida is 831, in Georgia is 308, in Hawaii is 41, in Idaho is 33, in Illinois is 643, in Indiana is 277, in Iowa is 130, in Kansas is 105, in Kentucky is 159, in Louisiana is 173, in Maine is 82, in Maryland is 322, in Massachusetts is 622, in Michigan is 409, in Minnesota is 326, in Mississippi is 109, in Missouri is 281, in Montana is 40, in Nebraska is 108, in Nevada is 92, in New Hampshire is 66, in New Jersey is 426, in New Mexico is 86, in New York is 1,255, in North Carolina is 405, in North Dakota is 42, in Ohio is 542, in Oklahoma is 118, in Oregon is 175, in Pennsylvania is 745, in Rhode Island is 82, in South Carolina is 157, in South Dakota is 32, in Tennessee is 275, in Texas is 800, in Utah is 115, in Vermont is 33, in Virginia is 287, in Washington is 314, in West Virginia is 89, in Wisconsin is 271, and in Wyoming is 18.