3.1 Quality control and diagnosis
At this point, one of the biomedical scientists will examine the section under the microscope to ensure that it is the correct type of tissue, corresponding with that noted on the form. They will also check that the sectioning and staining has been carried out properly (Figure 11). If it is not, repeating the sectioning and staining will be necessary. The whole of this process, from the time that the tissue arrives in the laboratory until the time that stained slides are ready to be examined takes one day.
At this stage a pathologist examines the slides - usually the pathologist who directed the original cut-up of the tissue. They may be examining up to 120 slides in a day, so the amount of time available for each one is quite limited. Here again, experience is very important in rapidly identifying the characteristic appearance of a disease process. The pathologist's report on the slide is dictated to audio, for transcription by medical secretaries, who may add this information to the original pathology request form. In many cases, however, the pathologist's report will be transcribed directly back to the central patient's record, which is held electronically.
Also at this time, the pathologist may identify additional tests that they want done on the tissues; for example, sections from additional areas of the block, different histochemical stains or immunohistochemistry. Perhaps 15 per cent of the blocks will require further examinations. The variety of additional tests is quite large (~40 different stain types, and ~80 different immunohistochemistry stains, although this will depend greatly on the laboratory and its speciality); consequently many of the additional stains are done individually, by hand, by the laboratory staff, although the more commonly used stains may be done by machine. Standard protocols are used, but the large number and variety of tests that are being done means that great accuracy and careful time management is needed to carry out this work; five to ten different staining protocols may be carried out by one person in a single session. In some laboratories immunohistochemistry is partly automated by the use of a machine that takes the sections through the successive antibody treatments, wash steps and final enzymatic staining. The results from the additional assays are again examined by the pathologist and reported back onto the patient record, which is now available to the clinician who requested the histology.
Tissue and sections that are taken for histology are retained in archive for at least twenty-five years, so that they can be reviewed again if necessary. The archives of any pathology laboratory are extensive and the filing of the material is a major activity. Many laboratories store older material off-site, because of space considerations.