TYPES OF PATHOLOGY LABORATORIES
The function of hospital pathology laboratories (Table 1.3) is to make scientific investigations of disease. The typical pathology service offered by hospitals has six main branches: medical microbiology, immunology, clinical biochemistry, hematology, histopathology and clinical genetics.
Types of pathology laboratories
Medical microbiology is concerned primarily with the detection and identifica-tion of pathogenic microorganisms. For clinical purposes, these consist of viruses, bacteria, protozoa, fungi and helminths (worms). Microorganisms are detected directly in specimens obtained from the patient or on swabs (for example throat, nasal) that are cultured in growth medium to increase the number of microorganisms and allow their easier detection. The presence of microorganisms may also be determined indirectly by detecting antibodies produced by the patient in response to the infection. Medical microbiology laboratories also investigate the responses of pathogenic microorganisms to antibiotics.
Immunology laboratories are concerned with studying the body’s immuneresponse in both healthy and diseased states. Immune responses are ‘cell-mediated’ or ‘humoral’. The former involves T lymphocytes, the latter the production of antibodies by specialized B lymphocytes. The presence or absence of antibodies in plasma can be determined, for example, by serum electrophoresis (Figure 1.9) to assess generalized immunodeficiencies and other diseases. However, of more diagnostic value during the investigation of immune diseases may be the measurement of specific antibodies that are produced in response to a particular antigen (which may be an infectious agent or an autoantigen). The number of cells involved in immunity, such as T-cells, B-cells, T-helper and T-suppressor cells, are often determined as this can provide valuable information about the immune status of an individual.
Clinical biochemistry is concerned with investigating the biochemicalchanges associated with diseases. A wide range of substances or analytes are measured in clinical biochemistry laboratories. Some of these analyses are carried out routinely on all samples (blood, urine) coming into the laboratory using automated methods (Figure 1.10); others need to be requested specially. Analyses include those for proteins, enzymes, hormones, lipids, tumor markers, blood gases, sugars and inorganic ions to investigate a variety of disorders, including those associated with abnormal renal, respiratory, metabolic, bone and endocrine function. In addition, analytes are measured during investigations of genetic disorders both to diagnose and to monitor the effectiveness of therapies.
Hematology is concerned with the study of disorders of blood cells, includingblood clotting (coagulation) defects. Hematological investigations can involve determining the concentrations of blood proteins, such as hemoglobin, to aid in the diagnosis of diseases. The microscopic examination of blood films, thin layers of blood spread out on a microscope slide and stained (Figure 1.11) and marrow removed from bone cavities by aspiration (Figure 1.12) may also be helpful. Some hematology laboratories may also be involved in the provision of blood and blood products for transfusion services, but these are often run as separate services.
Histopathology is concerned with the investigation of disease by examiningcells and tissues. This involves the macro- and microscopic investigation of body tissues for the identification of disease. Amongst other things, histopathology laboratories are usually involved in the diagnosis of malignancies and can also provide information on how far a tumor has progressed (‘staging’) and therefore can suggest a likely prognosis. In addition, histopathology laboratories may also assist with investigation of a range of infectious and inflammatory conditions affecting body tissues.
Clinical genetics is a growing area in the investigation of diseases. A major focusof clinical genetics laboratories is the identification of genetic abnormalities This could include, for example, identifying the number and form of chromosomes (Figure 1.13) in blood films to identify any numerical and structural abnormalities.