Practice Questions Flashcards
The organisation responsible for accrediting diagnostic histopathology laboratories in Australia is the:
a) National Association of Testing Authorities
b) Royal College of Pathologists of Australasia
c) National Association of Testing in Australia
d) National Pathology Accreditation Advisory Council
e) Australian Institute of Medical Scientists
A - National Association of Testing Authorities
The optimal tissue section thickness for specimens prepared for electron microscopy is:
a) 2-5 μm
b) 30-50 μm
c) 60-90 μm
d) 2-5 nm
e) 60-90 nm
E - 60-90nm
Name the 8 types of staining.
- Non-vital
- Vital/phagocytic
- Histochemical
- Lysochrome
- Impregnation
- Injection
- Fluorochrome
- Immunostaining
Describe non-vital staining.
Staining of dead tissue that’s been fixed, processed and sectioned. (Bulk of routine staining - HandE)
Describe vital/phagocytic staining.
Living tissues/cells, less toxic because of dilute dyes or phagocytic action of macrophages ingesting the dye particles. (Eg. Janus Green)
Describe histochemical staining.
Used to visualise biological structures. Tissue must be fixed. (Eg. PAS)
Describe lysochrome staining.
Stains neutral lipids and fats. Stains dissolve into fats. (Eg. Sudan Black and Oil O Red)
Describe impregnation staining.
Example is reticular staining with the use of silver salts. The silver salts are reduced to form black coating/deposit around the individual fibres. They require a reducing agent. (Eg. Reticular stains)
Describe injection staining.
Not technically a stain but classed as one. Injection of coloured compound (not always a dye) to highlight structures. (Eg. Latex dye)
Describe fluorochrome staining.
Fluorescent molecules combined with a tissue entity is visualised under fluorescent light. (Eg. Fluorescent antigen technique)
Describe immunostaining.
Antibody-antigen labelling. A labelled antibody is used. (Eg. Direct and indirect IHC).
What is a chromophore?
A colour bearer. Atomic groupings which are required for a stain to work. The more chromophores within a compound, the deeper the colour.
Eg. Quinonoid, Azo and Nitro groups
What is an auxochrome?
Ionizing group which gives the dye a net positive charge.
It assists the dye to bind to the tissue itself. It can also intensify the colour.
- If auxochrome gives net +ve charge = basic/cationic dye
- If auxochrome gives net -ve charge = acidic/anionic dye
Eg. Hydroxyl, methyl and amino groups.
What are 7 stains for liver biopsies and what do they test for?
- H and E: general structure
- Orcein: Hep B antigens
- PAS: Glycogen storage
- PAS-D: Neutral mucins, (adenocarcinomas secrete neutral mucins.)
- Reticulin: Reticular fiber general tissue architecture and changes therein = cirrhosis.
- Perls: Iron deposits and haemachromatosis
- Van Gieson: Collagen increased in cirrhosis.
What is a modifier?
They are additions of various side groups to the dye molecule which can enhance or change the dye colour. Eg. Eosin B or Eosin Y
What is a leuco compound?
A colourless solution which destructs the chromophore (reduces) to make the compound more soluble. They are oxidised in a subsequent reaction to add colour.
They produce a colour on contact with a certain tissue element that it’s trying to bind to.
Eg. Schiff’s reagent
What is the difference between regressive and progressive staining?
Regressive is when you OVER stain and then differentiate by removing excess stain. Progressive staining is when stain applied until the desired intensity of tissue coloration is attained.
What is a trapping agent?
A chemical which inhibits removal of dyes from tissues. Eg. Iodine in gram staining
What is differentiation?
Removal of excess stain (as in regressive staining) or using differentiation agents to distinguish between multiple tissue components.
Differentiation agents include mordants, acids and oxidising agents.
What can depth of colouration be affected by?
- Chemical affinity
- Density
- Permeability and diffusion of dye.
What is trichrome staining?
A staining method that uses two or more acid dyes in conjunction with a polyacid. Three different dyes of 3 different particle sizes will penetrate the tissue differently depending on density, chemical affinity and permeability.
Why use a weak positive control?
A weak positive is going to show up a result, but only just and this means our tests will be very sensitive.
Which stain has a copper atom at its centre?
Toluidine blue
What is the difference between antigen and antibody?
Antigens are molecules capable of stimulating an immune response.
Antibodies are Y shaped proteins produced by B cells of the immune system in response to exposure to antigens.
How does formalin work?
It works by cross linking the amino acid side chains within the tissue.
What are 4 benefits of IHC autostaining?
- Standardisation
- Onboard antigen retrieval
- Integrated IT system
- Digital image capture
What are the benefits of using IHC stains?
- Sensitive and specific
- Results are more consistent/highly reproducible
- Doesn’t require tissue to be fresh
- Can study almost any Ab
What is a sentinel node?
The closest lymph node to a tumour is usually the 1st site of metastases.
Ideal fixative type?
Generally 10% neutral buffered formalin
What is an advantage of using microwave HIER (Heat induced epitope retrieval)?
It’s very cheap
What are two disadvantages of using microwave HIER (Heat induced epitope retrieval)?
- The time depends on the microwave wattage
- Hot and cold spots
What are some advantages of using pressure cooker HIER (Heat induced epitope retrieval)?
- Very few hot and cold spots
- No evaporation
- Can accommodate large number of slides
- Short incubation period at higher boiling point (120C)