You may have heard the term “pathology” being used by doctors, especially if you have been treated in hospital.  But what exactly is pathology?  And what has it to do with the law?  Pathology is the study of disease, and it involves the analysis of body tissue including organs, cells, bodily fluids and their constituents.  The discipline of pathology is subdivided into a number of smaller areas of specialisation, each with their own particular focus; each of these deserves a book in their own right, but I shall aim to summarise them below.  From a legal perspective, clinical errors can occur in each sub-speciality and may result in a clinical negligence claim.


Haematology is the study of disorders of the blood and a specialist in haematology is called a haematologist.  There are three primary cellular aspects of blood that are of importance: red blood cells (which carry oxygen around the body), white blood cells (which fight infection and are involved in immunity) and platelets (which are involved in bleeding and clotting).

Most haematologists will treat all disorders of the blood, but some specialist haematologists are experts in particular disorders. Probably the most well-known disorder of the red blood cells is anaemia, although there are many different types of anaemia not caused just by blood loss due to bleeding.  Abnormalities of the white blood cells can cause leukaemia, a haematological cancer, and abnormalities of the platelets can cause bleeding disorders (e.g. haemophilia), if there are too few platelets, or thrombosis/clotting disorders (e.g. deep vein thrombosis), if there are too many.  Haematologists may also specialise in haematological cancers, such as multiple myeloma, leukaemia or lymphoma, and such specialists are known as haematological oncologists; other speciality areas for haematologists are bone marrow failure (e.g. aplastic anaemia) and bone marrow transplantation.

Abnormalities of the blood cells can be identified from the taking of a sample of blood for a Full Blood Count (FBC), a routine and straightforward but often crucially important investigation.  There are also many other more complex and sophisticated investigations that haematologists can carry out to investigate blood disorders.  Clinical errors involving haematology may result from a simple failure to interpret correctly the FBC, resulting in a delay in diagnosis of a particular haematological condition (such as anaemia) and its underlying cause, leading to delayed treatment, or the inappropriate treatment of a particular disorder such as myeloma or lymphoma, amongst others.

Chemical pathology (also biochemistry or clinical chemistry)

The body contains a huge number of both simple and complex chemicals found in the cells, blood and other bodily fluids.  Chemical pathologists study the body’s biochemistry and test and report on many of these various substances, including electrolytes (sodium (Na+), potassium (K+), calcium (Ca2+), etc.), hormones (oestrogen, testosterone, thyroxine, etc.), glucose (for diabetes, in particular), enzymes, proteins, drug levels, and many others.  These can assist with the diagnosis and management of a whole host of diseases and illnesses.  Along with the FBC, some very useful blood tests can be performed as routine investigations, commonly known as U&E (urea and electrolytes), LFT (liver function tests), and bone and kidney function tests.  Biochemistry tests can also identify some of the rarer, inherited metabolic disorders.

A chemical pathologist is unlikely to be particularly involved in a clinical negligence case but, on occasion, their expertise may be required in a specific situation, e.g. in a case of hyperlipidaemia or hyperthyroidism, diabetes, or involving an unusual metabolic disorder.  However, a clinical error more commonly may be made by a non-specialist doctor misinterpreting a biochemistry blood result.


Histology is the study of tissue; histopathology the study of diseased tissue.  A histopathologist is a specialist who reviews and interprets tissue samples taken from patients to aid in the clinical diagnosis of a particular condition or disease, its severity and extent.  These samples can be reviewed at the macroscopic level, i.e. visible to the naked eye, and at the microscopic level, i.e. viewed under a microscope or using other even more detailed imaging techniques (such as electron microscopy).  The tissue samples upon which a histopathologist relies are usually obtained by way of a biopsy by a patient’s treating clinician; a common example is a biopsy of a gastric ulcer during a gastroscopy procedure.

Forensic histopathologists (“pathologists”) also carry out post mortems, either commissioned by the hospital in which the patient has died or by a Coroner.  Post mortems and their findings may be very relevant to the holding of an Inquest, when a patient has died of an uncertain cause, or to a clinical negligence claim, as an aid to the underlying cause of an avoidable death.

From a legal perspective, a histopathologist may make a mistake as to what is identified in a particular tissue sample, resulting in the failure to appreciate the nature and/or extent of a cancer or other disease, for example, leading to a missed opportunity for early treatment.


Cytology is the study of cells; specialists in this field are called cytologists.  Cytopathology is the study of diseased cells and is especially important in cancer: it is the cytopathologist who studies the cells from a cervical smear to look for cervical cancer or cervical intraepithelial neoplasia (CIN), a possible cancer pre-cursor.  Cytologists review cells obtained from a tissue biopsy or fine needle aspiration (FNA) and, in the context of clinical negligence, as with a histopathologist, a cytopathologist may misinterpret findings and fail to diagnose a condition such as cancer.

Infectious diseases

The study of infectious diseases includes the study of bacteria (microbiology), viruses (virology), parasites (parasitology) and tropical diseases.  Specialists in these areas of pathology are involved in the diagnosis, management and control of infection.  This is a huge area of medicine in its own right.  It is also a hugely important area, given the number of diseases that are borne and caused by bacteria, viruses and other similar organisms, for example influenza or tuberculosis (TB).

Well-known serious bacterial infections include pneumonia, meningitis and endocarditis, and specialist microbiologists are able to advise on the diagnosis and management of such conditions.  Medical microbiologists are also especially important in managing hospital-acquired infections, including MRSA (Methicillin-resistant Staphylococcal aureus) and Clostridium difficile (“C diff”) infections.   They are also very important in the management of TB.  Virologists study viral infections, including the childhood viruses, such as mumps, measles, rubella (MMR), chicken pox, etc. and Human Immunodeficiency Virus (HIV), Herpes Simplex (HSV) and other viruses.  Parasitologists study parasites, which are mainly infections caught abroad, including tape worms, etc.  Medical mycologists study fungi and Tropical Diseases specialists study tropical infections, including malaria, typhoid, typhus, yellow fever, and dengue fever, which are rare in this country but which can be extremely serious.

Clinical errors in most infectious diseases are not common but, when they do occur, they can be catastrophic, because some of the diseases can be very aggressive if not recognised and treated quickly.  Legal claims from cases involving meningitis, endocarditis and TB, for example, are usually against general practitioners or hospital staff not familiar with the symptoms and signs of such rapidly progressive conditions rather than the specialists in infectious diseases.  Nevertheless, the outcome from such diseases can be so catastrophic that early recognition and treatment, with input from an infectious disease specialist, is often critical.


Immunology is the study of the immune system; specialists in this area are called immunologists and they are involved in the diagnosis and treatment of common allergies, for example, peanut allergy or drug allergies, rarer immunodeficiency syndromes, autoimmune diseases and organ transplantations.  However, many immunological conditions are very rare and immunologists are unlikely to be involved in a clinical negligence claim very often.


Geneticists are specialists in the field of genetics and they study hereditary conditions, such as cystic fibrosis, and the transmission of genes.  Clinical cytogeneticists carry out the microscopic analysis of chromosome abnormalities looking for conditions such as Down’s Syndrome, whereas molecular geneticists use the tools of DNA technology to analyse mutations in genes.  There are many genetic or inherited conditions, or conditions with a genetic element, with more being discovered all the time, and increasingly geneticists are being involved in the use of genetics in treatment for diseases such as cancer.

In the clinical negligence context, a geneticist may fail to identify an abnormal mutation in a chromosome on analysis, resulting in a disabled child, for example, leading to a wrongful birth claim.

Stem cells

Stem cells are an increasingly important part of pathology and a relatively new field of medicine, regenerative medicine, has essentially grown up around their research.  Hailed in the late ‘90s as the new technology that would result in whole organs being grown and transplanted within a decade, progress has not in reality been quite so rapid.  However, where progress has been made in stem cells is in the use of living cells as therapies, aiming to prevent problems in the first place rather than replace an organ when it has failed.  Recent research has been carried out to good effect with stem cells.  In the medicolegal context, stem cell technology has yet to make its mark, as it is probably too embryonic in its development.  However, there is little doubt that, as the science progresses and stem cell biotechnology becomes increasingly mainstream, there will be legal as well as ethical and moral isues and dilemmas occurring.