Clinical pathology is a branch of medicine concerned with the diagnosis of disease based on the laboratory analysis of tissue and fluid (blood, urine, body cavities).
Whereas surgical pathology arose from surgeons needing to know more about the tissues they encounter and resect, clinical pathology arose from internal medicine specialists interested in the application of modern laboratory methods to their patients’ conditions. Clinical pathology emerged as five somewhat distinct laboratory areas.
The first to evolve was microbiology, and the others include hematology, chemistry, immunology and blood bank/transfusion medicine. With the advent of our understanding of chromosomes, genes and DNA, molecular pathology is emerging as the newest field. It understandably bridges clinical and anatomic pathology.
Blood Bank and Transfusion Medicine
Transfusion medicine is concerned with the transfusion of blood and blood components. The blood bank is the section of the clinical laboratory where medical technologists process and distribute blood products.
The blood donor center is the facility that collects and processes blood products. Physicians certified in transfusion medicine are trained in blood product selection and management, immunohematology, apheresis, stem cell collection, cellular therapy and coagulation.
Clinical chemistry is generally concerned with chemical analysis of bodily fluids. Using modern automated analyzers, as well as traditional techniques such as electrophoresis, spectrophotometry and chromatography, the Clinical Chemistry Laboratory supports physicians in diagnosing diseases and monitoring treatment.
Data generated by the laboratory, plus the interpretation of this data, assists in defining diseases with biochemical etiologies and in elucidating biochemical mechanisms of diseases or response to treatment. As experts in chemical test methodology, clinical biochemistry’s relation to disease mechanisms and quantitative analysis, clinical chemists interact with a wide variety of physicians to assist in test development and interpretation of results.
Though closely aligned with chemistry, diagnostic immunology centers on various diagnostic techniques that rely on the specificity of antigen antibody reactions. Requiring a basic knowledge of the immune system, this laboratory is concerned with detection of minute amounts of chemical substances. It requires a basic knowledge of the immune system and its response to antigen.
Using antibodies conjugated with a fluorescent, chromogenic or radioactive “label,” antigens can be detected with high sensitivity and specificity. A variety of detection methods include immunofluorescence, immunofixation and electrophoresis, nephelometry, enzyme-linked immunoassay, agglutination, immunodiffusion, complement fixation and others. In addition to evaluations of the humoral immune system, evaluations of the cellular immune system are performed in more specialized immunology laboratories.
Microbiology deals with the study of microbial organisms including bacteria, viruses, fungi and parasites. The clinical microbiology laboratory uses a variety of culture, immunologic and molecular techniques to evaluate diseases thought to have an infectious basis. Clinical microbiologists and technologists work closely with infectious disease physicians to evaluate patient samples for both individual diagnosis/treatment as well as epidemiologic population studies.
An important aspect of the laboratory is assistance in selecting antimicrobial drug therapy based on testing of the offending organism’s susceptibility to various drugs that might be used for treatment. Clinical microbiologists are increasingly versed in both traditional laboratory techniques and emerging applications of molecular test methods.
Hematopathology is concerned with diseases of the blood and blood forming tissues. At the interface between anatomic and clinical pathology, hematopathology incorporates both morphologic and bench laboratory methods in evaluating neoplastic and non-neoplastic abnormalities involving red blood cells, white blood cells, platelets and coagulation proteins.
Traditional microscopy of peripheral blood films, body fluids, bone marrow aspirates and biopsies and lymph nodes is augmented by newer techniques such as flow cytometry and molecular and cytogenetic testing. Additionally, clinical laboratory hematology testing centers on automated blood cell analysis, evaluation of disorders related to blood coagulation and evaluation of red blood cell disorders such as hemoglobinopathies.
Hematopathologists work closely with clinical hematologists/oncologists as well as other physicians in consultation over hematologic testing.