The clinical pathology specialty laboratories include hematology, microbiology, immunology, clinical chemistry (and toxicology), the blood bank (transfusion medicine), and laboratory data management. In these areas, the pathologist acts as a consultant to the clinician, defining appropriate tests and interpreting their results. Many of these tests solidify a clinical diagnosis. After diagnosis, many tests are performed repeatedly to assess progress of the disease and response to treatment.
In clinical hematology, for example, pathologists review all abnormal blood smears. They may also obtain bone marrow samples from patients. In examining the smears and microscopic sections from these sources, the pathologist may encounter problems as diverse as the identification of malarial parasites or other blood-borne organisms, investigation of causes of anemia, detection of disorders of coagulation, and definitive diagnosis of malignant diseases such as leukemia.
In most hospital settings the pathologist is in charge of the blood bank and functions as an immunohematologist, who is in charge of procurement and processing of blood and blood products. The responsibilities include monitoring the use of blood within the hospital, tracing the causes of transfusion reactions, testing for determinants of tissue compatibility that permit bone marrow and other transplants, and serving as a consultant to plan appropriate therapy for a wide variety of conditions.
In clinical chemistry, the pathologist supervises the technical staff in performance of tests to determine the concentration of organic and inorganic substances and medications in body fluids. For example, the level of glucose (sugar) in blood or urine is needed to diagnose diabetes and to monitor the daily insulin dosage. Supervision of the use of instruments and maintenance of a strict system of quality control are essential to assure accurate laboratory determinations. Toxicology is often part of the clinical chemistry service, involving the pathologist in therapeutic drug monitoring and detection of illicit drugs and poisons. In cases of infection, the microbiology laboratory identifies the offending organism and tests to discover which antimicrobials are capable of killing or arresting the growth of that particular agent (bacteria, viruses, parasites).
Testing for immune reactions and allergies is a growing area of laboratory activity. Allergic and toxic reactions to foreign materials have long been recognized, but many recently identified diseases reflect immune responses to normal body proteins, that are either altered or present in abnormal locations. Immune functions are also critical in toleration of transplanted tissues or organs.
Other areas of responsibility of the clinical pathologist are the development of comprehensive information systems and the maintenance of quality control and quality assurance procedures. Both are needed to ensure economical use of the clinical laboratory, to enable the development of new testing and appropriate utilization of existing services, while maintaining a high quality of medical care. Pathologists constantly seek ways to achieve greater accuracy, precision, specificity and sensitivity of laboratory tests. Information systems are needed to handle the enormous volume of test information correctly attributed to each individual patient, and provide the correct ranges of normal values for each test in that laboratory, while maintaining patient confidentiality. Quality control checks on the accuracy of test results, whereas quality assurance aims to provide prompt, efficient collection and rapid availability of test results to the treating physician.
Wright stain of a post-transplant bone marrow. Reprinted with permission from Archives of Pathology & Laboratory Medicine. (Arch Pathol Lab Med 2006;130:1482) Copyright 2006. College of American Pathologists.