A-level Applied Science/The Role of the Pathology Service
About this Unit
From the AQA Specification:
You will need to produce a portfolio of evidence which considers the work undertaken by the following departments in the pathology service: biochemistry, haematology, microbiology and pathology.
You will then undertake a microbiological analysis, and either a chromatographic or electrophoresis analysis.
How you will be assessed
This unit is assessed through the work you complete for your portfolio.
The marking criteria are found in the AQA specification.
What you need to know
Pathology is the study of the processes underlying disease and other forms of illness, harmful abnormality, or dysfunction. Within biology but also a branch of medicine, it means specifically the study and diagnosis of the structural and functional changes in cells, tissues and organs that underlie disease. Pathology as a field of knowledge hence forms the basis of the scientific reasoning behind the practice of medicine.
Scope of pathology
The primary goal of pathology is the study of the four main aspects of a disease:
- Etiology: what causes the disease
- Pathogenesis: the mechanism by which a certain etiological factor causes disease
- Morphologic changes: the structural changes induced in the cells, tissues and organs
- Clinical significance: the functional consequences of the morphologic changes
Because the public rarely meets pathologists, their work is not well understood. Pathology is a large and diverse field that allows a pathologist to participate in multiple areas of the field or focus their scope to a specific area.
Essential to everyday surgeries, pathologists are responsible for processing and reporting on all specimens generated during surgery. Tissue samples are taken from the submitted specimens, stained, and processed for microscopic evaluation. Microscopic examination searches for disease of any type and this information is returned to the surgeon via a pathology report.
Pathologists are also responsible for laboratory specimens. They, along with medical technologists, process specimens at medical laboratories for interpretations. In other words, when a doctor refers to a "laboratory result", they are not referring to a number generated by a black box; instead, it is the interpretation of a value by a pathologist or a technologist. It is also important to understand that a different laboratory might produce a different value on the same specimen.
Pathologists are also called upon to perform autopsies. Autopsies represent less than 5% of the workload of a typical modern pathologist. There exists a subspecialty in pathology that allows for the training of medical examiners who wish to pursue forensics.
Pathologists usually do not see patients, but do on occasion such as when performing bone marrow biopsies and aspirates or fine needle aspirations of superficial nodules. Thus, pathology is best considered a form of diagnostic medicine.
In addition to the diagnosis of disease, including cancer, and the administration of medical laboratories, pathologists often participate in the teaching of medical students (Pathology is a core course in the medical curriculum).
Pathologists express their opinion as a pathology report addressed to the doctor requesting it. Since pathologists most often communicate with other doctors, they are sometimes nicknamed "the doctor's doctor".
Pathology is often considered the most scientific branch of medicine because of the available avenues of research involving human material.
Finally, the circulation of laboratory data is a central issue in medical informatics and the current tendency towards electronic medical records.
Tools of pathology
The techniques used most often in the study of the disease process and hence diagnosis are:
- Gross pathology: the recognition of disease based on macroscopic examination of surgical specimens generated at the time of surgery or at autopsy.
- Histology: the microscopic study of tissues. Histopathology is the science of diagnosing diseases on the basis of the histological aspect of the diseased tissues.
- Cytology: the study of detached cells. Cytopathology is the science of diagnosing diseases on the basis of the cytological aspects of detached cells. The most common application of this technique is the Pap smear.
- Clinical chemistry: the gathering, detection, and reporting of an incredible array of chemical measures found by the analysis of collected body samples.
- Immunology: the use of specific immune markers and antibodies to aid in the diagnosis of disease.
- Flow cytometry:analysis of a process that allows for the identification of specific cells .
- Molecular Biology techniques, like PCR and Fluorescent in situ hybridization (FISH) are increasingly useful to diagnose diseases, especially microbiological and cancer diagnosis.
In the United States, pathologists are medical doctors (MD) or doctors of osteopathic medicine (DO), that have completed a four year undergraduate program, four years of medical school training, and four to five years of postgraduate training in the form of a pathology residency. Training may be within two primary specialties, as recognized by the American Board of Pathology:
- Anatomic Pathology, the science of diagnosing diseases based on the appearance, both gross and microscopic appearance of tissues.
- Clinical Pathology, the science of diagnosing diseases based on the analysis of body fluids like blood, urine, etc.
Most pathologists seek a broad based training in both fields and thus require five years of postgraduate training known as residency. Finally, a board certification examination is required. Boarding requirements are set by the American Board of Pathology. Pathologists, like all other medical doctors, are also required to meet continuing medical education requirements.
A pathology laboratory (medical or clinical laboratory) is a laboratory where tests are done on biological specimens in order to get information about the health of a patient.
Types of laboratory
In many countries, there are two main types of labs that process the majority of medical specimens. Hospital laboratories are attached to a hospital, and perform tests on these patients. Private (or community) laboratories receive samples from general practitioners, insurance companies, and other health clinics for analysis.
For extremely specialised tests, samples may go to an environmental science or research laboratory.
A lot of samples are sent between different labs for uncommon tests. It is more cost effective if a particular laboratory specialises in a rare test, receiving specimens (and money) from other labs, while sending away tests it cannot do.
Sample processing will usually start with a set of samples and a request form.
Typically a set of vacutainer tubes containing blood, or any other specimen will arrive to the laboratory in a small plastic bag, along with the form.
The form and the specimens are given a laboratory number. The specimens will usually all receive the same number, often as a sticker that can be placed on the tubes and form. Entry of requests onto a laboratory management system involves typing, or scanning (where barcodes are used) in the laboratory number, and entering the patient identification, as well as any tests requested. This allows laboratory machines, computers and staff to know what tests are pending, and also gives a place (such as a hospital department, doctor or other customer) for results to go.
. For biochemistry samples, blood is usually centrifuged and serum is separated. If the serum needs to go on more than one machine, it can be divided into separate tubes.
Many specimens end up in one or more sophisticated automated analyser, that process a fraction of the sample and return one or more "results".
Laboratories today are held together by a system of software programs and computers that exchange data about patients, test requests and test results, known as a laboratory information system.
This system enables hospitals and labs to send the correct test requests for each sample and keep track of individual patient or sample history, and help to guarantee a better quality of results, as well as publishing the results for doctors to check and patients to read.
- Important publications in pathology.
- Blood test values - gives an idea of which specialisms work with which tests.
The Medical Research Council publishes a series of Review Updates which includes disease mechanisms and their diagnosis.
Public Health Laboratory Service and Centre for Communicable Diseases, Colindale Avenue, London.
- Fosberry R, Human Health and Diseases, Cambridge Modular Sciences series, Cambridge University Press, ISBN 0-521-42159-4;
- Lowrie, P. and Webb, S. Microbiology and Biotechnology, Cambridge Modular Science series, Cambridge University Press, ISBN 0-521-42204-3;
- Wymer, P, Practical Microbiology and Biotechnology in Schools, Macdonald & Co publishers, ISBN 0-356-11566-6;
- Williams, R.E.O. Microbiology for the Public Health, Public Health Laboratory Service, London, ISBN 0-901-14418-5;
- Sattaur, O. The New Genetics, Inside Science, New Scientist, 3 December. No. 16, p1-4. New Scientist, P.O. Box 666, London E15 1DW;
- Vile R. Cancers and Oncogenes, Inside Science, New Scientist, 10 March. No. 32, p1-4. New Scientist, P.O. Box 666, London E15 1DW;
- Brown, P. AIDS the Challenge of the Future, Inside Science, New Scientist, 18 April. No. 54, p1-4. New Scientist, P.O. Box 666, London E15 1DW;
- Cambell-Platt G. The Food We Eat, Inside Science, New Scientist, 19 May. No. 10, p1-4. New Scientist, P.O. Box 666, London E15 1DW;
- Collee G. Food Poisoning, Inside Science, New Scientist, 21 October. No.27, p1-4. New Scientist, P.O. Box 666, London E15 1DW;
- D.T.Plummer, An Introduction to Practical Biochemistry, McGraw-Hill, ISBN 0-07-084165-9;
- K. Mannion and T. Hudson. Collins Advanced Modular Science (CAMS) – Microbes, Medicine and Biotechnology, Collins Educational. ISBN 0-00-322392-2;
- Nuffield Science in Practice. GNVQ Science Assignments Advanced, Heinemann. ISBN 0-435-63254 X;
- Nuffield Science in Practice. GNVQ Science Assignments 2 Advanced, Heinemann. ISBN 0-435-63255-8;
- P. Wymer. (1987) Practical Microbiology and Biotechnology for Schools, McDonald & Co, on behalf of the Society for General Microbiology. ISBN 0-356-11566-6.
The Royal College of Pathologists, 2 Carlton House Terrace, London, SW1Y 5AF.
When accessing healthcare related information on the internet candidates and teachers are strongly advised to check the reliability and currency of the data obtained.
Many of the larger charities who fund research into diseases have excellent web resources. The Government publishes guidelines (National Institute for Clinical Excellence) and has developed the National Service Frameworks, all of which are available on-line as PDF files.
The British Medical Journal provides free access to journal publications a year in arrears.
Many large teaching hospitals and universities have good web pages.
- Florida State University Internet Pathology Laboratory.
- Kansas University Histology resources.
- University College London; Biochemistry of Health & Diseases
Other informative sites
- Biotechnology and Biological Sciences resources.
- Merck manuals - Medical information online.
- Online Biology textbook.
- eMedicineHealth (First Aid guidance).
- Protein electrophoresis.
- British Medical Association A-Z of resources.
- Immunohistochemistry protocols and troubleshooting