Pathology, branch of medicine concerned with determining the nature and course of diseases by analyzing body tissues and fluids. Pathology is divided into anatomic and clinical pathology. Anatomic pathologists perform autopsies and analyze tissues taken from patients during surgery or by biopsy. Clinical pathologists contribute to the diagnosis of disease by measuring chemicals and cells in blood, sputum, bone marrow, and urine.
As knowledge of human biochemistry and metabolism proliferated in the 20th century, many more laboratory tests were devised to distinguish normal states from disease states. Among the important tests are the measurement, by machine, of chemicals such as sodium, potassium, urea, and glucose in the blood; the similarly automated counting of various types of cells in the blood; and the determination of compounds in the urine, which can help diagnose kidney disease. Identification of the types of cells in the bone marrow and blood contributes to the diagnosis of some types of cancer.
Pathologists also direct the correct use of blood for transfusions, determine suitability for transplantation of organs such as kidneys (see Transplantation, Medical), and perform tests to identify various types of blood-clotting disorders. Microbiology laboratories, which test for the presence of pathogenic bacteria and viruses in the blood and tissues, are likewise under the direction of pathologists. In addition, they test for deficiencies in immunity. A special discipline called forensic pathology is concerned with analyzing medical evidence in crimes. See also Microscopic Anatomy; Bacteriology; Blood; Cytology; Disease; Histology; Immune System.