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1 What are the main artefacts seen in pre-analytical procedures and how can they be prevented?
Answer:
The main artefacts are broadly categorised under two groups:
- Tissue dehydration prior to fixation issues
- Mechanical trauma or damage to the tissue due to surgical procedures which directly affects the tissue. These would include
- Crushing/pinching effects of the tissue from the forceps used to remove the tissue sample from the patient
- Leaching of autolytic lysozymes from ruptured cells resulting in localised tissue damage
- Fragmentation of the tissue
- Haemorrhagic changes as a result of rupturing blood vessels.
Following good surgical practice will reduce the incidence of these artefacts, including consideration of the following:
- Adequate depth of the specimen to avoid fragmentation
- Fast and efficient fixation immediately following tissue removal.
- Appropriate handling of the tissue sample including delicate use of forceps or even using a suture as an alternative to forceps.
- In instances of small incisional biopsies and small delicate strips of tissue placing the tissue on card or sponges and then immersing in fixative will reduce the curling and shrinking effect.
- Avoidance of sources of foreign bodies as a result of the surgical process.
- Careful attention to the effects of heat and drying artefacts due to electrical cautery instruments or from lasers.
2 Describe the two main groups of artefacts that can occur when undertaking a surgical procedure and subsequently performing histological assessments. How do we group artefacts that occur in the laboratory?
Answer:
The two main groups of artefacts are
pre-analytical and post-analytical artefacts.
We can classify the laboratory-based artefacts under the following headings:
- Fixation
- Specimen dissection
- Tissue processing
- Embedding
- Microtomy
- Staining both tinctorially and immunocytochemically
- Coverslipping and mounting of tissue sections
- Automated machine failures resulting in defects in dehydration (processing machines), embedding (tissue embedding machines), staining (automated stainers) and coverslipping (automated coverslippers).
- Molecular contamination artefacts
- Miscellaneous causes.
3 Explain cross-contamination of specimens during the specimen dissection, processing and embedding stages of routine histological investigations. What procedures do we have to ensure the incidence of these artefacts is kept to a minimum?
Answer:
This relates to the unintentional transfer of
tissue fragments or indeed cells from one patient sample to
another. It can occur at several points in the laboratory based
procedures, but most commonly the specimen dissection, processing
and embedding and staining steps.
The incidence can be avoided by careful attention to:
- Standard operating procedures
- Cleanliness and good laboratory practice
- The use of logs to record how many pieces of tissue are placed in each cassette
- Good in house quality control checks.
4 Explain the various artefacts that can occur during tissue microtomy and how these can be avoided.
Answer:
The main artefacts seen following microtomy include:
- Knife marks and scores
- Trimming artefacts including chatters/venetian blind effects
- Tissue folds/creases
- Tissue displacement issues
- Entrapped water bubbles under tissue sections
- Squames floating on the waterbath and being picked up with tissue sections
- Water contamination in the waterbath.
These artefacts can be avoided by ensuring microtome blades are sharp. Sections are cut appropriately and floated out on water baths. The use of softening agents such as Cellsoft to improve sectioning of harder tissues should be advocated. Attention to good microtomy practice to ensure no tissue cross contamination occurs during the section floating out stages should also be applied.
5 What are the types of artefacts that can be produced from automated procedures? What measures should the laboratory staff employ to minimise the incidence of such artefacts?
Answer:
These include:
- Processing machine or staining machine breakdowns resulting in incomplete processing or staining.
- Inadequate or contaminated reagents on automated machines.
- Human error related to loading of reagents or consumables required on automated machines.
- Overheating of slides or tissue due to faulty thermostatic control or monitoring.
In order to reduce the incidence of these artefacts, the following should be considered:
- Ensure all service records for all machinery are in date.
- Keeping good records of reagent management and knowing when reagents need to be changed.
- Ensure all logs of procedures are available to be assessed to enable error traceability.
- Clear training in the use of automated equipment and the provision of adequate supervision for trainees using such equipment
- Competence checks on staff using automated machinery
- Attention to detail in manufacturer information on how to operate the equipment
- Appropriate attention to in-house standard operating procedures
- Robust internal and external quality control checks.