Laboratory Diagnosis of Infectious Disease Flashcards
What do you need to ensure if you’re going to send a tissue sample?
You send in correct transport medium
You check patient data is correct
If there is more than one sample you identify the sites of both/all
You ensure that the pathologist has enough information as to where to sent the report back to
You ensure that you understand & act on the result that is generated
What is pathology/histopathology/cellular pathology?
The study of disease & the process by which you obtain a diagnosis from a tissue sample
What is cytopathology?
Method of visualising cell structure where fluids, scrapings or aspirations are examined
Provides predictive but not equivalent information to histology
Quick, simple, cheap- serious complications are rare
If you get a large sample that won’t fit into one cassette, do you examine it as one piece
No, you’ll most likely have to dissect it into smaller pieces to see what’s going on in the different areas.
What needs to happen from the tissue in the pot to the tissue on the slide so that it can be assessed microscopically?
You need to embed that tissue in a very hard and rigid substance (wax) so you can then attach that onto the microtone & use a very sharp blade to get the really fine sections
Then put the very fine pieces of tissue into a warm water bath & dip a slide in- it’s very easy to collect that fine slice of wax which contains the tissue and get the lab number immediately onto the slide so you don’t lose identification
Then, routine stain with H&E
What steps are involved in a routine histological diagnosis?
slides
How do you ensure that the wax is allowed to permeate and embed itself right into the tissues?
Dehydrate the tissue by putting them into an overnight processor
What extra work might need to be done when diagnosing from a slide?
More H&E stained sections because:
-cannot see a lesion that fits the clinical picture
-biopsy difficult to interpret
-being super cautious and checking there is nothing sinister
-biopsy not put in the wax in the right way and the orientation of the tissue is making assessment difficult
What are some special stains used in pathology and what for?
PAS- fungi, salivary mucin/mucus
Grocott- fungi
Elastin- blood vessel architecture
ZN (Ziel Neelson)- mycobacteria (TB)
Gram- bacteria
Trichrome- collagen
What is immunohistochemistry?
Immunohistochemistry (IHC) refers to the process of selectively visualising antigens (e.g. proteins) in cells of a tissue section by exploiting the principle that antibodies bind specifically to antigens in biological tissues.
When is immunohistochemistry used?
Tumour pathology:
Different types of normal and tumour cells express different antigens
Tag the antibody with a chromogen– reaction occurs on antigen binding and can be seen on tissue section
Technique can be used in tissues that have been fixed in buffered formalin
What are some examples of chromagens in immunohistochemistry and what tumours they would stain?
slides
Are there any tests in which the biopsy should not be sent in formalin?
Frozen sections- immediate intra-operative diagnosis
Direct immuno-fluorescence
Tissue to be banked for future research
How can you genetically test for tumours?
Can dissect tumour cells from an unstained section taken from a paraffin block and use even more specialised techniques to look for chromosomal changes
Not relevant for majority of tumours but a small proportion do have reproducible and single genetic abnormalities
E.g. Ewings sarcoma has a reproducible translocation between chromosomes 11 and 22
What is direct immunofluorescence?
A special technique used to confirm the diagnosis of immunological diseases that can occur in the oral cavity
Biopsy tissue sent in a special medium- Michel’s medium
