Pathology and laboratory medicine
Pathology contributes to diagnosis through direct examination of specimens and oversight of laboratory testing. Its work includes checking results, improving specimen handling, interpreting findings and helping clinical staff use the laboratory.
The pathologist’s role
A pathologist is a physician who has completed a pathology residency after a medical degree and may also have fellowship training. In the United States, anatomic and clinical pathology each have their own board-certification examination. In 2008, the United States had approximately 13,000–14,000 board-certified pathologists.
Almost every patient entering the US healthcare system receives some care from a pathologist, although that contribution often takes place behind the scenes. Surgical pathology and cytopathology receive less public attention than autopsy despite their major role in care.
Divisions of pathology
Pathologists directly perform anatomic pathology tests and usually oversee testing in clinical pathology. The subdivisions include the following.
| Division | Subdivisions |
|---|---|
| Anatomic pathology: surgical pathology | Gastrointestinal, liver and pancreas; genitourinary and reproductive; breast; respiratory; cardiovascular; head and neck; endocrine; musculoskeletal; soft tissue; skin; nervous system; lymph nodes and spleen |
| Anatomic pathology: cytopathology | Cytopathology |
| Anatomic pathology: autopsy | Nonforensic; forensic |
| Clinical pathology | Clinical chemistry; medical microbiology; transfusion medicine; body fluid analysis; therapeutic drug monitoring; coagulation; toxicology; immunology; haematology (blood and bone marrow); molecular pathology |
Cytopathology examines very thin layers of cells and is closely related to, and sometimes considered part of, surgical pathology. Samples may be scraped from a superficial surface, as in a cervical smear, or obtained by needle aspiration. Aspiration of superficial breast or thyroid lesions can use palpation as a guide; deeper lesions, such as liver masses, require imaging. Cytopathology may provide a definitive diagnosis but often provides a preliminary diagnosis later correlated with a larger tissue sample, when available.
Autopsy is postmortem examination. After natural death it may establish the cause or extent of disease or document disease-related changes. All pathologists are trained in autopsy, while forensic pathologists have additional training in medicolegal investigation, including biological and physical evidence, wound patterns and identification. Their work can include examining living people and providing public health and safety services as well as criminal investigations.
In clinical pathology, specially trained technologists obtain, prepare and test biological samples, performing procedures such as blood counts, chemistry profiles, urinalyses, cultures and blood typing. They also run, maintain and troubleshoot complex instruments; pathologists generally oversee quality and consistency.
The divisions overlap: haematology often connects blood and bone marrow analysis with examination of lymph nodes and spleen in surgical pathology. Molecular diagnostics further blur these divisions by complementing microscopic, biochemical, chromosomal and immunological studies, particularly in malignant disease.
Practice settings
Facility size usually determines the breadth of a pathologist’s testing responsibilities. In a small community hospital, one pathologist may perform all surgical pathology examinations and autopsies and oversee clinical pathology, sending specialised tests to private reference laboratories, academic institutions, state laboratories or the Centers for Disease Control and Prevention. Larger medical centres allow subspecialisation in one or a few categories, while PhD specialists may run clinical pathology areas and pathologists often direct the laboratory overall. Pathologists work alongside laboratorians ranging from assistants with basic training to highly specialised staff.
In large practices, some pathologists spend most of their time on administration, while others maintain consultation practices for difficult cases. Teaching and academic posts may involve training residents and students, preparing lectures, writing grants, publishing and research.
Specimen handling
Accurate laboratory results depend on specimen collection timing and technique, labelling, suitable containers and preservatives, and prompt delivery. Pathologists help identify and improve problems along this chain, including those arising outside the laboratory.
For example, for the most accurate drug-concentration results, blood must be drawn after a steady state between intake and excretion; measurement of peak-to-trough fluctuation also requires specified timing relative to the last dose. An accurately assayed sample collected at the wrong time may fail to describe drug handling, so a pathologist can draw attention to mistimed collection.
A sample labelled sputum from a patient with pneumonia may instead be saliva, lacking lower respiratory tract secretions. Culture may then yield no organisms or organisms unrelated to the infection; a pathologist can alert staff to the need for appropriate collection.
Quality, communication and education
Pathologists help produce timely, accurate and relevant results through quality monitoring, specimen procedures, communication and education. Quality work may include reviewing clinical results and critical values, re-examining blood smears already reviewed by technologists, reviewing microbiological cultures and smears, and consulting on transfusion. Both divisions inspect and revise procedure manuals, supervise new tests and review interlaboratory comparison performance; pathologists and technologists also inspect other laboratories.
Pathologists communicate new test methods, policy changes and changes to outdated ordering practices through individual discussions, teaching, written instructions and interdepartmental meetings. They interpret results with clinical staff and liaise with outside services, such as specialist toxicology or coagulation laboratories, regional blood centres and the CDC for unusual organisms. They also connect the laboratory with administrators over space, service expansion and technology, and convey users’ needs back to the laboratory.
Teaching laboratorians may cover diseases, the relation between clinical conditions and laboratory testing, and interpretation of tests such as Gram stains and blood smears. Pathologists also teach staff outside the laboratory how to use its services.
Molecular methods and interpretation
By 2008, flow cytometry was established for characterising leukaemias and lymphomas, and use of polymerase chain reaction and hybridisation was increasing across surgical pathology, microbiology, forensics and inherited disease.
Even simple tests require laboratory support and expert interpretation, roles for which pathologists are trained. For example, a proposed credit-card-sized blood test strip read by colour changes would still require attention to test-pack integrity, sample handling and application, controls, correlation with other methods and investigation of unexpected findings.