What Is Pathology? Branches, Methods, Societies, and Careers

Pathology is the study of disease. In medicine it is the specialty that diagnoses disease by examining tissues, cells and body fluids; in the research laboratory it is the discipline that asks how disease arises and progresses. The word covers both a clinical service and a scientific field, which is why one search for it returns hospital laboratories, journals, training programs and research funding all at once. This guide separates those meanings, explains the main branches, and shows where pathology touches the laboratory regulation, biobanking and research administration topics covered elsewhere on CASRAI. It is an educational overview, not medical advice: nothing here should be used to interpret a personal diagnosis or pathology report.

What Is Pathology?

At its simplest, pathology links what is seen in a sample to what is happening in a patient. A surgeon removes a tumor, a clinician draws blood, a hospital performs an autopsy; in each case a pathologist or laboratory scientist examines the material and reports what it shows. The same habit of mind drives the research side of the field, where investigators examine tissues from patients and from experimental models to work out the mechanism behind a disease rather than only to name it.

Two points of vocabulary help from the start. A pathologist is normally a physician who has completed specialty training in pathology; the people who run tests, prepare slides and operate analyzers are laboratory professionals such as technologists and histotechnologists, and many research pathologists hold a PhD rather than a medical degree. And pathology is a laboratory specialty: many pathologists never see patients in a clinic, yet their reports often decide what treatment a patient receives. Pathology as a recognized medical specialty is comparatively modern; general references describe it as being treated as a distinct specialty by roughly the late 1920s to early 1930s.

Anatomic vs. Clinical Pathology

The traditional division in clinical pathology practice is between two broad halves, and the American Board of Pathology certifies in each: Anatomic Pathology, Clinical Pathology, and a combined AP/CP certification.

• Anatomic pathology diagnoses disease through the gross, microscopic, chemical, immunologic and molecular examination of organs and tissues. It is the world of biopsies, surgical specimens, cytology samples and autopsies.
• Clinical pathology (often called laboratory medicine) diagnoses and monitors disease through laboratory analysis of blood, urine and other body fluids, and oversees the laboratories that perform those tests.

The boundary is practical rather than absolute. A leukemia diagnosis, for example, may combine a blood count (clinical pathology), a bone marrow biopsy (anatomic pathology) and molecular testing that belongs to both; the field of hematopathology sits across the line. See What Is Hematology? for the clinical specialty that works alongside it.

Experimental and Research Pathology

Experimental pathology, also called investigative or translational pathology, uses the tools of pathology to study the biology of disease. Where a diagnostic pathologist asks what is this lesion?, the experimental pathologist asks why did it form, and what changes at the cellular and molecular level? The work spans human tissue studies, animal models, cell culture and computational analysis, and it overlaps with cancer biology, immunology, neuroscience and toxicology.

Typical research questions include how tissue architecture changes as a tumor develops, which molecular markers distinguish disease subtypes, how inflammation and fibrosis damage an organ, and how a candidate drug alters tissue in a preclinical study. Research pathologists also serve as the tissue experts on many large projects, from clinical trials to genomics consortia. See What Is Genomics? for the sequence-level companion discipline.

Major Subspecialties

Within anatomic pathology the field is divided by organ system and technique. General references list the following among the main branches:

• Surgical pathology — examining tissue removed at surgery or biopsy, the largest part of routine anatomic practice.
• Cytopathology — examining individual cells or small clusters, for example from fluid samples or fine-needle aspirates.
• Histopathology — the microscopic study of diseased tissue, built on tissue sectioning and staining.
• Dermatopathology, neuropathology, pulmonary pathology and renal pathology — organ-focused subspecialties.
• Forensic pathology — investigation of sudden, unexpected or suspicious deaths. See What Is Forensic Science? for the broader field.
• Hematopathology — diagnosing blood and bone marrow disease, bridging the two halves of the specialty.
• Molecular pathology — using DNA, RNA and protein testing to classify disease and guide therapy.
• Oral and maxillofacial pathology — diseases of the mouth, jaws and related structures.

Clinical pathology similarly includes areas such as clinical chemistry, microbiology, transfusion medicine and immunology, though the exact labels differ between training programs and countries. The American Board of Pathology also lists subspecialty certification and focused practice designations beyond its primary certificates; consult the board directly for the current list rather than relying on any secondary summary.

Histology and the Path From Specimen to Diagnosis

Histology, the study of tissue structure, is the technical backbone of anatomic pathology. A typical workflow runs as follows:

1. Collection and accessioning. The specimen is labeled, logged and linked to the patient and request. Labeling errors are a recognized hazard; see Specimen Labeling Error Prevention.
2. Gross examination. The pathologist or a trained assistant describes the specimen and selects representative pieces.
3. Fixation and processing. Tissue is preserved, then embedded in a supporting medium so it can be cut into very thin sections.
4. Sectioning and staining. Thin sections are mounted on slides and stained. The workhorse stain is hematoxylin and eosin; see H&E Staining: Hematoxylin and Eosin Explained.
5. Special studies. Immunostains, in situ hybridization and molecular tests add detail the routine stain cannot show.
6. Interpretation and report. The pathologist reviews the slides and issues a signed report to the treating clinician.

Research laboratories add specialized tools. Laser capture microdissection isolates selected cells from a tissue section for molecular analysis. Microscopy itself is changing: digital pathology scanners convert glass slides into whole-slide images that can be reviewed on screen, shared between sites and analyzed by software, and the practical questions of buying one are covered there. Image-analysis and AI tools build on those digital slides, and the data-handling side overlaps with health informatics. Pathology is not the same discipline as imaging-based diagnosis; compare What Is Radiology?.

The waste produced along this workflow, including tissue and fixatives, has its own handling rules; see Pathological and Anatomical Waste Disposal.

Biobanking and Tissue Resources

Pathology departments are the natural custodians of human tissue. Residual diagnostic material, along with blood and other samples collected for research, can be stored with associated clinical data and made available to investigators. A biobank is an organized collection of such materials, and a biospecimen is an individual sample within it; a tissue bank is the tissue-focused version. Pathologists decide what tissue can be spared from diagnosis, confirm what a sample actually is, and annotate it so that it is scientifically useful.

Research use of human samples raises consent and governance questions that research administrators handle directly. For the consent models in use, see Biobank Specimen Consent Models and the entry on informed consent; for reuse of existing material, see Secondary Use of Identifiable Data and Biospecimens. Operational choices such as inventory systems are covered in Biobank Software, and one large, widely used resource and its access tiers are described in UK Biobank Data Access. On quality, ISO 20387 is the international standard for biobanking, and the College of American Pathologists runs a biorepository accreditation program; see CAP-BAP. In the UK, tissue handling falls under the Human Tissue Act.

Laboratory Regulation: CLIA and CAP

Because pathology results drive patient care, the laboratories that produce them are regulated. Two names come up constantly in the United States, and they are often confused.

CLIA, the Clinical Laboratory Improvement Amendments, is the federal program that sets quality standards for laboratory testing performed on human specimens. Congress passed it in 1988; it applies to testing done to assess health or to diagnose, prevent or treat disease, and its requirements scale with the complexity of the test method. The Centers for Medicare & Medicaid Services oversees the program. It is a legal requirement rather than a voluntary label. For the certificate types and complexity categories, see CLIA Certification and CLIA High Complexity Testing Requirements.

The College of American Pathologists (CAP) is a professional organization that describes itself as the leading organization of board-certified pathologists. It operates a laboratory accreditation program, proficiency testing and external quality assessment programs, and a biorepository accreditation program. CAP accreditation is a separate, voluntary peer-inspection process; see CAP Accreditation Checklist and CAP Proficiency Testing. An international standard, ISO 15189, covers medical laboratory quality and competence; see ISO 15189 Accreditation and the ISO 15189 vs CLIA comparison. Whether a particular research-only laboratory falls under CLIA depends on whether results are reported for patient care, so confirm with your compliance office rather than assuming.

Professional Societies and Journals

• College of American Pathologists (CAP) — the professional organization above, centered on laboratory quality and practice.
• American Board of Pathology (ABPath) — the certifying body for pathologists, with primary certification in anatomic pathology, clinical pathology, or both, plus subspecialty certification. It certifies individuals; it is not a society.
• USCAP (United States and Canadian Academy of Pathology) — an educational and research-oriented organization that holds an annual meeting and publishes Modern Pathology and Laboratory Investigation. It describes itself as a division of the International Academy of Pathology.
• ASIP (American Society for Investigative Pathology) — the society most closely associated with experimental pathology. It publishes The American Journal of Pathology, the Journal of Molecular Diagnostics and AJP Compendia, and hosts scientific meetings.

Many other societies serve individual subspecialties, from cytopathology to digital pathology to forensic pathology, and national societies exist outside the United States.

How Pathology Research Is Funded

In the United States, pathology research is supported mainly through the National Institutes of Health, with cancer-related work often funded through the National Cancer Institute, one of the NIH institutes. Because disease mechanisms cut across organs, pathology projects can be reviewed and funded by many institutes depending on the disease studied, so there is no single pathology funder. Other sources include foundations, disease charities, industry-sponsored studies and institutional funds. We have not verified current program names or budget figures for this guide; check each funder’s own site and the specific funding announcement before you plan an application.

For a researcher or administrator new to the process, What Is a Grant? is the general starting point. Pathology projects add predictable administrative tasks: human-subjects and tissue-use approvals, specimen consent review, material transfer arrangements, core facility charges for histology or scanning, and compliance with clinical laboratory rules where results reach patients. Budgeting for those items early prevents the most common delays.

Training and Careers

The main routes into the field are:

• Physician pathologist. A medical degree followed by pathology residency, then board certification in anatomic pathology, clinical pathology or both, and optional subspecialty training. Program length and requirements are set by the relevant accreditation and certification bodies; check the American Board of Pathology for the current rules.
• Physician-scientist or PhD investigator. Researchers studying disease mechanisms may enter experimental pathology through a PhD or combined MD-PhD, typically publishing in the journals above.
• Laboratory professionals. Medical laboratory scientists, histotechnologists, cytotechnologists and pathologists’ assistants run the technical work of the laboratory.
• Specialist roles. Biobank managers, digital pathology and informatics specialists, and laboratory quality and compliance staff.

Frequently Asked Questions

What does a pathologist do?

A pathologist examines tissues, cells and body fluids, and interprets laboratory results, to establish or confirm a diagnosis. Many also direct laboratories, supervise quality systems, and teach or do research.

What is the difference between anatomic and clinical pathology?

Anatomic pathology diagnoses disease from organs, tissues and cells; clinical pathology diagnoses and monitors disease from laboratory analysis of blood, urine and other fluids. Many pathologists are certified in both.

Is a pathologist a medical doctor?

Typically, yes: diagnostic pathologists are physicians who completed specialty training. Research pathologists may instead hold a PhD.

What is the difference between pathology and histology?

Histology is the study of normal tissue structure and the techniques used to prepare and examine it. Pathology uses histology, among other methods, to study and diagnose disease. When tissue is examined for disease it is called histopathology.

Is plant pathology the same thing?

No. Plant pathology studies diseases of plants and shares a name and some methods, but it is a separate field; see What Is Plant Pathology?.

Does a research lab need CLIA certification?

It depends on whether results are used to assess a person’s health or to guide care. Research-only testing is treated differently from patient testing, but confirm with your institution’s compliance office and the CLIA rules linked above.

How is pathology different from radiology?

Pathology examines physical samples removed from the body, while radiology interprets medical images of the living body. See What Is Radiology?.

Where can I read pathology research?

Major society journals include The American Journal of Pathology (ASIP), Modern Pathology and Laboratory Investigation (USCAP).