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2.1 Describe how sampling error might affect the reliability of a cytology report for the following types of specimen: (a) bronchial washings, (b) voided urine, and (c) FNA of a suspicious mass.
(a) Bronchial washings are intended to sample a wide surface area. Although the rinse fluid comes into contact with a larger surface area than other collection techniques there is the possibility that cells will not dislodge from tissues in sufficient quantity for reliable detection.
(b) Voided urine may contain cells from any part of the urinary tract. However, cells may not readily exfoliate and diagnostic cells may not appear in the final slide preparation.
(c) Excellent technique in fine needle aspiration is crucial for the avoidance of sampling error. If the needle does not enter the relevant tissue or if an incorrect aspiration technique is used then the final preparation may not be representative of the lesion being sampled.
2.2 Why is fixation of cytology specimens necessary?
To preserve cells in a lifelike state and to prepare them for subsequent demonstration techniques.
2.3 State the benefits and possible limitations of the direct smear technique.
Benefits:
- A simple and inexpensive technique.
- The cytologist is able to use clinical and technical judgement in selecting appropriate parts of the specimen to transfer to the slide.
- Cells are transferred directly onto the glass slide without risk of cell loss through intervening processing steps.
Limitations:
- Variable quality of preparations.
- Potential for sampling error.
2.4 Make a list of the various ways in which diagnostically important cells in cytology specimens can be concentrated onto a relatively small area of a glass slide.
- Large volume centrifugation
- Cytocentrifugation
- Density gradient centrifugation
- Gravity sedimentation
- Membrane filtration
- Cell blocks
2.5 Describe the purpose of the dyes used in the Papanicolaou technique.
Haematoxylin stains the nucleus of cells a dark blue colour. Eosin, light green and orange G stain the cytoplasm of cells pink, green, or orange.
2.6 List the similarities and differences between direct and indirect immunocytochemical methods.
Similarities:
- Both involve specific antigen-antibody interactions.
- The primary antibody links directly with the antigen of interest.
- A coloured molecule may be used as a label or tag. Alternatively, a colourless label may be used which can be converted into a coloured end product.
Differences:
- The indirect method involves signal amplification using secondary antibodies and is therefore more sensitive for antigen detection.
- The indirect method involves a greater number of processing steps.
2.7 List the similarities and differences between the three types of exhaust protective cabinet.
Similarities:
- All are designed to offer protection from airborne microorganisms, either to the worker or to the material being handled.
- All make use of a carefully regulated air flow and suitable filters.
Differences:
- Some are designed to protect the worker (e.g. class I), whilst others are specifically designed to prevent contamination of the material being handled (e.g. class II).
- Provide different levels of protection according to the microbial hazard group being handled. For instance, class I cabinets are designed for handling microorganisms in hazard groups 1–3, whereas class IV cabinets must be used for handling group 4 organisms).