Branch of medicine concerned with the nature, function, and diseases of the blood. It covers the cellular and serum composition of blood, the coagulation process, blood-cell formation, hemoglobin synthesis, and disorders of all these. Marcello Malpighi, in the 17th century, was the first to examine red blood cells (erythrocytes). In the 18th century, the British physiologist William Hewson (1739–74) examined the lymphatic system and blood clotting. In the 19th century, the bone marrow was recognized as the site of blood-cell formation, and diseases of the blood such as anemia and leukemia were identified. In the early 20th century, the ABO blood-group system was discovered and the role of nutrition in blood formation was studied. Post-World War II studies have delved further into the nature of blood diseases and improved treatments and have examined hemoglobin synthesis and the role of platelets in blood coagulation.
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Physicians specialized in hematology are known as haematologists. Their routine work mainly includes the care and treatment of patients with haematological diseases, although some may also work at the haematology laboratory viewing blood films and bone marrow slides under the microscope, interpreting various haematological test results. In some institutions, haematologists also manage the haematology laboratory. Physicians who work in haematology laboratories, and most commonly manage it, are pathologists specialized in the diagnosis of haematological diseases, referred to as haematopathologists. Haematologists and haematopathologists generally work in conjunction to formulate a diagnosis and deliver the most appropriate therapy if needed. Haematology is a distinct subspecialty of internal medicine, separate from but overlapping with the subspecialty of medical oncology. Haematologists may specialise further or have special interests, for example in:
''(Hema- comes from the Greek word "`'aima" meaning "blood", -ology means study of.)
In a clinical laboratory the hematology department performs numerous different tests on blood. The most commonly performed test is the complete blood count (CBC) also called full blood count (FBC), which includes; white blood cell count, platelet count, hemoglobin level and several parameters of red blood cells. Coagulation is a sub-speciality of hematology; basic general coagulation tests are the prothrombin time (PT) and partial thromboplastin time (PTT). Another common hematology test in the erythrocyte sedimentation rate (ESR).