Manual of basic techniques for a health laboratory - libdoc.who.int

3. General laboratory procedures 953.7.2 Fixation and dispatch of biopsy specimens forhistopathological examinationBiopsy specimensTo diagnose certain diseases of the organs, the physician removes a piece of tissuewith forceps or a special scalpel. This piece of tissue is called a biopsy specimen. It isexamined under the microscope after a thin section has been cut and treated witha special stain.HistopathologyThe cells of biopsy specimens from tissues and organs can be studied under themicroscope. This type of examination is called histopathology and can be mostimportant, particularly for the diagnosis of cancer.The laboratory technician must be able to fix the biopsy specimen and to ensurethat it is properly dispatched and arrives at the pathology laboratory in a good stateof preservation.Fixation of biopsy specimensThe piece of tissue is immersed in a fixative fluid. This procedure should preservethe tissue in a state as close to the living state as possible, by protecting it againstbacterial action, autolysis, shrinkage, etc.The most suitable type of bottle for biopsy specimens is a plastic-capped bottlewith a wide mouth (pill bottle). Such bottles are obtainable in 60-ml, 45-ml, 30-mland 15-ml sizes.FixativesFixatives that are simple to prepare are:— formaldehyde saline (reagent no. 27);— Zenker fixative (reagent no. 66). Just before use, add 5ml of glacial aceticacid per 100ml of Zenker solution.TechniqueAmount of fixativeThe volume of fixative required is about 50 times the volume of the biopsy tissue.Biopsy tissue is normally 3–5mm thick (if it is thicker, fixation is difficult orimpossible).The area of the specimen, however, can vary and this is what determines the amountof fixative to be used (see Table 3.3).Table 3.3 Calculating the amount of fixativeto use for biopsy materialDimensions of specimen (cm)Amount of fixative (ml)0.5 ¥ 0.5 6–100.5 ¥ 1 10–151 ¥ 1 20–252 ¥ 1 30–402 ¥ 2 90