What is pathology?
Pathology is a vital part of the practice of modern medicine. It is the way that many diseases are confirmed and may be how unexpected disorders are diagnosed. It is also used to measure the response to treatment. The extensive range of testing available is performed by expert pathologists, scientists and technicians, with service to patients and referring doctors being a priority. This commitment to high quality and rapid service assists the doctor in the accurate diagnosis and early treatment of disorders.
The staff at Pathology Queensland are vital members of a team caring for patients. There are 10 different areas of pathology:
- Blood Bank
- Molecular Pathology
A large number of disorders will result in changes in the level of the chemicals of the body. Biochemists measure a wide range of chemicals and assist doctors in the diagnosis of disease and maintenance of patient health. Chemicals commonly measured include sodium, potassium, cholesterol, glucose (e.g. for diabetes), hormones (e.g. for IVF), tumour markers and liver enzymes. Biochemistry also assists in the control of drug therapy. By measuring the levels of drugs in blood, it is possible to ensure that patients are taking the correct amount of medication. This is extremely important in disorders such as epilepsy and heart disease.
As a result of major surgery, trauma or chronic illness, many people require blood transfusions. The Australian Red Cross Blood Transfusion Service supplies blood and blood products from voluntary donors for use with these patients. To ensure compatible blood is transfused, a blood specimen is collected from the patient and is tested for a blood group and any unexpected red cell antibodies. Suitable donor blood is then selected and delivered to the hospital for transfusion.
This area investigates the chromosomal make-up of human cells. Chromosome abnormalities can cause congenital defects, mental retardation, failure to undergo puberty, recurrent miscarriage and infertility. Examples are Down syndrome and Klinefelter syndrome.
Certain small chromosome changes can be investigated using fluorescent labelled DNA probes (fluorescent in-situ hybridisation or FISH). Examples of these are Williams syndrome and Prader-Willi syndrome.
Chromosome abnormalities can be diagnosed prenatally at 12–16 weeks from amniotic fluid and 10–12 weeks from chorionic villi. FISH can be used prenatally to provide a rapid screen for the major abnormalities, such as Down syndrome. It is also the basis for pre-implantation genetic diagnosis of blastomeres in IVF programs.
Cytogenetic investigation is useful in studying cancer and leukaemia, where specific chromosome changes are associated with specific neoplasms, and can also assist with diagnosis and prognosis.
The cytologist's major role is the examination of cells for cancerous changes. Cells obtained from cervical screening tests, fine-needle aspirations of lesions, or body fluids such as urine are examined to detect the presence of abnormal cells. Cytologists can also provide rapid on-site evaluation of specimen adequacy to clinicians collecting fine-needle aspirations.
Haematologists examine blood and blood-forming tissues (bone marrow). The diagnosis of leukaemia is usually made by examining the white blood cells found in the blood and bone marrow. Examination of the red blood cells and haemoglobin, the protein that transports oxygen throughout the body, enables a diagnosis of anaemia to be made. Plasma, the fluid component of blood in which the cells are suspended, carries the factors responsible for the clotting of blood and sealing of broken blood vessels. For those patients who are undergoing treatment after open-heart surgery or a stroke, the control of their clotting ability is crucial. This is maintained by adjusting the dose of their medicine on the basis of their laboratory results.
Histopathologists examine tissue, removed during an operation or from skin biopsies (e.g. for melanoma), in order to diagnose cancer and a myriad of conditions ranging from infection to autoimmune disorders.
Antibodies circulating within blood identify and attach to foreign particles and assist in their destruction. The body's ability to produce antibodies is the key in its fight against disease. Without adequate levels of antibodies the body's defence is lowered. In autoimmune diseases such as rheumatoid arthritis, a person's immune system starts producing antibodies to their own tissues. Immunologists measure antibody levels and other factors in order to assess the patient's immune status. For allergy, a person's immune system is over-responsive to external stimuli (e.g. pollens, house dust mite).
Microorganisms such as bacteria, viruses, fungi and parasites are the major causative agents of infectious disease.
Microbiologists identify the microorganism(s) causing disease and perform antibiotic susceptibility testing of bacterial and some fungal pathogens. Clinical microbiologists assist referring doctors in the diagnosis and management of patients with infectious diseases.
Molecular Pathology involves the investigation of diseases/disorders at the DNA level. A revolutionary technique known as PCR* (Polymerase Chain Reaction) provides a rapid method for the generation of large quantities of relatively pure DNA sequences of interest. PCR is used in the diagnosis of inherited disorders (such as haemochromatosis), neoplasms (such as lymphomas), and infections (such as chlamydia). The Molecular Pathology Laboratory also offers bacterial strain typing using Pulsed Field Gel Electrophoresis (PFGE) for infection control or epidemiological purposes in healthcare settings (* PCR is a patented process owned by Hoffman-La Roche Inc).
In some diseases it is not possible to isolate the causative agent of infection in the laboratory. In these patients, the identification of antibodies (produced by the body in response to the disease) is the only way to establish which organism is responsible for the disease process. This method of diagnosis is used when diseases such as Ross River fever or rubella are suspected.
Royal College of Pathologists of Australia 2016, RCPA, Sydney, viewed 18 August 2016, [https://www.rcpa.edu.au/Home].