Specimen Processing (Histology)
Patient specimens may be received from several sources: the operating theatres, wards, endoscopy suites and outpatient clinics within the Norfolk and Norwich University Hospital and James Paget University Hospital, Cromer and District Hospital; from GPs from Norfolk and Suffolk and occasionally dentists. With over 58,000 specimens received annually it is essential that we can identify each specimen accurately.
Fixation and Processing
With the exception of frozen sections and a few other isolated examples, the vast majority of tissue samples are received in a fixative solution which halts the natural processes of autolysis (enzymatic destruction) and bacterial attack, and preserves the tissue to enable it to withstand further processing. This takes from a few hours to three days depending on the size and nature of the specimen.
Each specimen receives a unique laboratory number and both the request form (click here to access form ) and specimen are labelled. All specimen details are entered on a computer system. During the daily “cut ups” the pathologist or biomedical scientist selects and describes the tissue samples to be examined. Some specimens (for example biopsies) are processed whole, while larger specimens e.g. mastectomies, colonic and rectal specimens) have a few selected pieces removed. Each selected piece of tissue is placed in a small perforated plastic container with a lid. The plastic “cassette” receives the laboratory number.
“Processing” is the term used to describe the removal of water from tissues and its gradual replacement with molten paraffin wax.
The tissues are embedded in a wax block. When cool, the block is placed in a machine called a microtome. The wax block is passed against a very sharp blade and then sections obtained. Cutting sections is a skilled process requiring training and practice, and is carried out by the laboratory's technical staff. Sections are usually cut at around 5 microns thick – a micron is one thousandth of a millimetre!
To remove any creases the section is floated onto a warm water bath, then picked up on a glass slide and dried. The number of blocks cut every day varies from 300-500 or more and several sections may be taken from certain blocks.