HT Tissue Processing 2 — Questions and Answers
Question 1: Which dehydrating agent is considered most miscible with both water and paraffin, making it a common transitional fluid in processing?
- Acetone
- Isopropanol
- Dioxane (Correct answer)
- Ethanol
Correct answer: Dioxane
Dioxane is miscible with both water and paraffin wax, allowing it to serve as both dehydrant and clearing agent in a single step.
Question 2: What is the primary purpose of the clearing step in tissue processing?
- To remove formalin from tissue
- To replace dehydrant with a paraffin-miscible fluid (Correct answer)
- To harden the tissue
- To stain lipids before embedding
Correct answer: To replace dehydrant with a paraffin-miscible fluid
Clearing replaces the dehydrating agent with a substance miscible with paraffin wax, preparing tissue for infiltration.
Question 3: Over-dehydration of tissue in concentrated alcohol most commonly results in which artifact?
- Vacuolation of cytoplasm
- Tissue shrinkage and hardening (Correct answer)
- Incomplete paraffin infiltration
- Basophilic shift in nuclei
Correct answer: Tissue shrinkage and hardening
Prolonged exposure to high-concentration alcohols extracts water excessively, causing tissue to shrink and become brittle.
Question 4: Which vacuum level is most commonly used during automated vacuum-assisted tissue processing to improve reagent penetration?
- 100 mmHg
- 250 mmHg (Correct answer)
- 400 mmHg
- 760 mmHg
Correct answer: 250 mmHg
Approximately 250 mmHg (one-third atmosphere) is routinely used; deeper vacuum can cause tissue damage while shallower vacuum reduces benefit.
Question 5: A histotechnician notices that bone biopsy cores remain gritty after standard paraffin processing. The most likely cause is:
- Insufficient dehydration time
- Inadequate decalcification before processing (Correct answer)
- Excessive clearing agent exposure
- Low paraffin infiltration temperature
Correct answer: Inadequate decalcification before processing
Residual mineral calcium salts cause hardness; bone must be fully decalcified before routine paraffin processing to allow sectioning.
Question 6: What role does agitation play during automated tissue processing?
- It raises processing temperature to speed dehydration
- It prevents paraffin from solidifying in the bath
- It accelerates reagent exchange at the tissue surface (Correct answer)
- It reduces the need for intermediate alcohol grades
Correct answer: It accelerates reagent exchange at the tissue surface
Agitation refreshes reagent at the tissue-fluid interface, reducing the concentration gradient and speeding diffusion into the tissue.
Question 7: Which tissue component is most susceptible to loss during xylene clearing in routine paraffin processing?
- Proteins
- Nucleic acids
- Lipids (Correct answer)
- Polysaccharides
Correct answer: Lipids
Lipids are soluble in xylene and other hydrocarbon clearing agents and are extracted during this step unless special lipid-preservation protocols are used.
HT Tissue Processing 2
Which dehydrating agent is considered most miscible with both water and paraffin, making it a common transitional fluid in processing?