What is Pathology?

Pathology is the medical specialty concerned with the study of the nature and causes of diseases. It underpins every aspect of medicine, from diagnostic testing and monitoring of chronic diseases to cutting-edge genetic research and blood transfusion technologies. Pathology is integral to the diagnosis of every cancer.

Pathology plays a vital role across all facets of medicine throughout our lives, from pre-conception to post mortem. In fact it has been said that "Medicine IS Pathology".

Due to the popularity of many television programs, the word ‘pathology’ conjures images of dead bodies and people in lab coats investigating the cause of suspicious deaths for the police. That's certainly a side of pathology, but in fact it’s far more likely that pathologists are busy in a hospital clinic or laboratory helping living people.

Pathologists are specialist medical practitioners who study the cause of disease and the ways in which diseases affect our bodies by examining changes in the tissues and in blood and other body fluids. Some of these changes show the potential to develop a disease, while others show its presence, cause or severity or monitor its progress or the effects of treatment.

The doctors you see in surgery or at a clinic all depend on the knowledge, diagnostic skills and advice of pathologists. Whether it’s a GP arranging a blood test or a surgeon wanting to know the nature of the lump removed at operation, the definitive answer is usually provided by a pathologist. Some pathologists also see patients and are involved directly in the day-to-day delivery of patient care.

Currently pathology has eight major areas of activity. These relate to either the methods used or the types of disease which they investigate. For further information on each discipline please click on one of the following:

Anatomical Pathology is the branch of pathology that deals with the tissue diagnosis of disease. For this, Anatomical Pathologists need a broad-based knowledge and understanding of the pathological and clinical aspects of many diseases.

The tissue on which the diagnosis is made may be biopsy material taken from a patient in the operating theatre, on the ward or from an autopsy (post-mortem). The latter is a small but important component of the work for establishing the cause in cases of sudden or unexpected death, for examining disease progression, including the response to treatment or lack of a response, and in criminal cases (forensic pathology) helping police in their investigations. The work of most Anatomical Pathologists is, however, on tissue from living patients. A large part of this is the detection and diagnosis of cancer. A tissue diagnosis is essential before starting treatment involving major surgery, radiation or drugs, treatments which may have major side effects.

Modern Anatomical Pathologists examine not only samples of solid tissue, but also small specimens of  separated cells. This is the subspecialty of Cytology. The specimens include fluids and tissue smears mainly for diagnosis and prevention of cancer. The pathologist collects some of these samples themselves, for example, for the diagnosis of cancer of the breast or the prostate. Often this means that a certain diagnosis can be made before the patient has left the clinic. New methods also allow samples of either separated cells or small tissue fragments to be obtained from organs, such as the pancreas, situated deep within body cavities.


Chemical Pathology is another discipline in the field of Pathology which deals with the entire range of disease. It encompasses detecting changes in a wide range of substances in blood and body fluids (electrolytes, enzymes and proteins) in association with many diseases. In addition, it involves detecting and measuring tumour (cancer) markers, hormones, poisons and both therapeutic and illicit drugs. For example Chemical Pathologists are involved in assessing levels of iron in the blood, measuring the levels of enzymes that are released into the blood after a heart attack to help in the diagnosis, and in the measurement of certain proteins produced by cancers to monitor the response to their treatment.

As with the other clinical pathology specialities, the largest part of a Chemical Pathologist's day is typically spent in clinical liaison. This involves advising clinicians about the appropriate tests for the investigation of a particular clinical problem, the interpretation of results and follow-up, and the effect of interferences eg by therapeutic drugs on test results. The working day also has a large component devoted to the validation and interpretation of test results, particularly for unusually abnormal results or more uncommon and highly specialised tests.

Evaluation of new technology and the development of new tests is an ongoing process in Chemical Pathology. This applies particularly to areas that are now opening up, such as the use of molecular biology techniques in diagnostic tests. Specialist areas of interest include such topics as inherited metabolic diseases, trace metals and environmental monitoring, drugs of abuse, and nutrition.

Forensic Pathology is the subspecialty of Pathology that focuses on medicolegal investigations of sudden or unexpected death.

A Forensic Pathologist is primarily involved identifying the cause of death and reconstructing the circumstances by which the death occurred. This is performed in a meticulous, painstaking manner. A major component of the role involves the performance of autopsy examinations to both the external and internal body organs to discover cause of death. They also look at tissue sample from bodies under the microscope to assist in establishing the underlying pathological basis for the cause of death.

Forensic Pathologists are occasionally required to visit crime scenes or accidents or to testify in court.

A General Pathologist is familiar with the major aspects of all branches of laboratory medicine described above. He or she is usually trained in anatomical pathology, cytology, chemical pathology, microbiology, haematology and blood banking, though not in as much detail as subspecialists in each field. A general pathologist would usually work in a medium sized private practice, community hospital or a large country town or other non-metropolitan centre. For problems demanding specific expertise they would consult with more specialised colleagues.

Some, however, also work as part of the team in large metropolitan public or private practices particularly in managing common high volume tests from more than one discipline.

The two main branches of genetic pathology are:

Biochemical Genetics which includes,

  • Population-based screening for inborn errors of metabolism by enzyme, protein and metabolite assays; and, diagnostic screening for inborn errors of metabolism in symptomatic patients by analysis of metabolites such as organic acids and amino acids;
  • Diagnostic assays for specific disorders by analysis of specific analytes in body fluids, enzymatic studies, or DNA studies of specific genes;
  • Predictive assays in unaffected relatives (or a fetus) to determine the risk of developing the disorder known to be present in the family;
  • Pedigree analysis and diagnostic assessment of segregation in kindreds of disease-causing mutations or genomic regions
  • Monitoring the biochemical status of patients for long term care or to guide acute care in metabolic crises.

Medical Genomics which includes,

  • Diagnostic detection and interpretation of genomic/ epigenomic variants in symptomatic patients (children, adults, fetuses);
  • Pedigree analysis and diagnostic assessment of segregation in kindreds of disease-causing mutations or genomic regions;
  • Diagnostic detection and interpretation of mosaic genomic variants, e.g. in cancer, pregnancy, and inherited diseases (e.g. tumour material; constitutional mosaicism; fetal DNA in maternal blood, circulating tumour DNA etc.) and quantitative assessment of mosaic genomic variants;
  • Predictive/pre symptomatic assays in unaffected relatives (or a fetus) to determine the risk of inheritance of a familial disorder;
  • Population-based screening for genomic abnormalities (antenatal and newborn screening programs);
  • Application of probability, statistics, bioinformatic databases, and other aspects of computer science relevant to the practice of genetic pathology.

Haematology is another rapidly developing discipline which deals with many aspects of those diseases which affect the blood such as anaemia, leukemia, lymphoma, and clotting or bleeding disorders.

Another important activity is the management of blood transfusion services. Many haematologists are involved, not only in the laboratory diagnosis and management of patients with blood diseases, but as clinical consultants. They also provide advice on the diagnosis and management of patients referred to them by medical colleagues, where the disease impacts on some aspect of the patient's blood.

In general terms, it is the variety and diversity of activities undertaken by haematologists at both a laboratory and clinical level, which provides the major attraction of this discipline.

Immunology is a specialty, like haematology, which often involves  both laboratory medicine (the testing of specimens collected from patients) and clinical practice (interviewing, examining and advising patients about clinical problems).

In the laboratory, immunologists are involved in the design, performance and supervision of tests of the immune system. These include, for example, testing for "allergy antibodies" (IgE) to determine whether patients have allergies to various substances, the measurement of different classes of antibody proteins to determine the state of the immune system's defence mechanisms, or monitoring the level of T-lymphocytes, the cells that disappear after HIV infection.

Clinical activities of an Immunopathologist include providing advice on a wide variety of other disorders including recurrent miscarriage and some areas of transplantation medicine. They may also be directly involved in managing patients with autoimmune diseases and AIDS

Microbiology deals with diseases caused by infectious agents such as bacteria, viruses, fungi and parasites. Microbiologists have roles both in the laboratory and directly in patient care. It offers involvement in a spectrum of activities ranging across:

  • basic laboratory science
  • direct patient care
  • public health
  • infection control
  • research and teaching
  • business management

The last two decades have seen enormous change in Medical Microbiology. 'New' organisms (Helicobacter pylori, HIV, Hepatitis C virus) have been discovered and characterised. 'New' infectious diseases (AIDS, Lyme disease, and Legionnaires' disease) have been described. 'Old' infections (tuberculosis, malaria, and pertussis)have re-emerged as major threats and have become increasingly resistant to previously effective antibiotics (MRSA, Streptococcus pneumoniae, VRE).

Over this time, advances in technology and molecular medicine (automation, polymerase chain reaction) have added greatly to the Microbiologist's diagnostic armamentarium. At the same time however, Microbiology remains very much a 'hands-on' discipline. In many ways it is an art as much as a science, and one in which an individual pathologist's experience, judgment and interpretive skills are pivotal.

Clinical aspects involve control of outbreaks of infectious disease and dealing with the problems of infections caused by antibiotic-resistant bacteria.


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