HT Specimen Handling & Fixation 2 — Questions and Answers
Question 1: Which fixative is MOST appropriate for preserving glycogen in tissue sections?
- 10% neutral buffered formalin
- Bouin's fixative (Correct answer)
- Carnoy's fixative
- Zenker's fixative
Correct answer: Bouin's fixative
Bouin's fixative (picric acid, formalin, acetic acid) preserves glycogen well and is commonly used for this purpose.
Question 2: A biopsy specimen arrives in the lab after a 6-hour delay without fixative. What is the MOST likely consequence?
- Increased nuclear detail
- Autolytic tissue degradation (Correct answer)
- Enhanced antigen retrieval
- Improved RNA preservation
Correct answer: Autolytic tissue degradation
Without fixation, endogenous enzymes continue to digest cellular components, leading to autolysis and loss of tissue architecture.
Question 3: The recommended tissue-to-fixative volume ratio for optimal formalin fixation is:
- 1:1
- 5:1
- 1:10 (Correct answer)
- 1:20
Correct answer: 1:10
A minimum 1:10 tissue-to-formalin ratio ensures adequate fixative penetration and complete fixation.
Question 4: Which of the following BEST describes the mechanism of formalin fixation?
- Protein denaturation by heat
- Cross-linking of amino groups via methylene bridges (Correct answer)
- Precipitation of proteins by alcohol
- Oxidation of sulfhydryl groups
Correct answer: Cross-linking of amino groups via methylene bridges
Formaldehyde reacts with amino groups on proteins to form methylene bridges, creating cross-links that stabilize tissue structure.
Question 5: Which fixative is CONTRAINDICATED when performing acid-fast staining for mycobacteria?
- 10% neutral buffered formalin
- Zenker's fixative (Correct answer)
- B-5 fixative
- Glutaraldehyde
Correct answer: Zenker's fixative
Zenker's fixative contains mercuric chloride, which can interfere with acid-fast staining results and requires extra processing steps.
Question 6: What is the PRIMARY advantage of using glutaraldehyde as a fixative for electron microscopy?
- Faster penetration than formalin
- Superior ultrastructural preservation (Correct answer)
- Better immunohistochemical antigen preservation
- Lower toxicity to laboratory staff
Correct answer: Superior ultrastructural preservation
Glutaraldehyde's bifunctional aldehyde groups create extensive cross-links that preserve ultrastructure for electron microscopy better than other fixatives.
Question 7: When receiving a lymph node specimen for lymphoma workup, which handling protocol is MOST important?
- Immediately place the entire node in formalin
- Submit fresh tissue for flow cytometry before fixation (Correct answer)
- Fix in B-5 fixative for 24 hours minimum
- Freeze all tissue for molecular studies only
Correct answer: Submit fresh tissue for flow cytometry before fixation
Lymphoma workup requires fresh tissue for flow cytometry, cytogenetics, and molecular studies, so a portion must be submitted fresh before any fixation.
HT Specimen Handling & Fixation 2
Which fixative is MOST appropriate for preserving glycogen in tissue sections?