HT Routine & Special Staining Methods 2 — Questions and Answers
Question 1: In the Periodic Acid-Schiff (PAS) reaction, periodic acid acts by:
- Oxidizing vicinal diols to aldehydes (Correct answer)
- Reducing Schiff reagent to release magenta dye
- Hydrolyzing glycogen to glucose subunits
- Decolorizing background with sodium metabisulfite
Correct answer: Oxidizing vicinal diols to aldehydes
Periodic acid oxidizes vicinal diol groups in polysaccharides to aldehydes, which then react with Schiff reagent to produce a magenta color.
Question 2: Which control tissue is most appropriate when validating a Gomori methenamine silver (GMS) stain for fungi?
- Lung tissue with confirmed Aspergillus infection (Correct answer)
- Normal liver tissue
- Skin with melanocytes
- Kidney with basement membranes
Correct answer: Lung tissue with confirmed Aspergillus infection
Lung tissue with confirmed Aspergillus provides positive fungal organisms to verify that GMS is correctly staining fungal cell walls black.
Question 3: The Warthin-Starry stain is used primarily to demonstrate:
- Helicobacter pylori and spirochetes (Correct answer)
- Acid-fast mycobacteria
- Gram-positive cocci
- Viral inclusion bodies
Correct answer: Helicobacter pylori and spirochetes
Warthin-Starry is a silver impregnation method that blackens spirochetes and organisms such as Helicobacter pylori against a yellow-brown background.
Question 4: In the Masson trichrome stain, the sequence of dyes applied after Weigert's iron hematoxylin is:
- Biebrich scarlet-acid fuchsin, then phosphomolybdic/phosphotungstic acid, then aniline blue (Correct answer)
- Aniline blue first, then Biebrich scarlet, then acid fuchsin
- Phosphomolybdic acid alone, then aniline blue
- Acid fuchsin, then aniline blue, then acetic acid only
Correct answer: Biebrich scarlet-acid fuchsin, then phosphomolybdic/phosphotungstic acid, then aniline blue
After nuclear staining with Weigert's hematoxylin, cytoplasm/muscle is stained red with Biebrich scarlet-acid fuchsin, then collagen is differentiated and counterstained blue with aniline blue.
Question 5: Which reagent is used to differentiate (decolorize) background in the Ziehl-Neelsen acid-fast stain?
- 1% acid-alcohol (Correct answer)
- Lugol's iodine
- Scott's tap water substitute
- Lithium carbonate
Correct answer: 1% acid-alcohol
1% acid-alcohol removes carbol fuchsin from non-acid-fast elements, leaving only mycobacteria stained red.
Question 6: Congo red stained amyloid deposits exhibit which optical property under polarized light?
- Apple-green birefringence (Correct answer)
- Maltese cross birefringence
- Negative birefringence only
- No birefringence
Correct answer: Apple-green birefringence
Amyloid stained with Congo red shows characteristic apple-green birefringence under cross-polarized light due to its beta-pleated sheet configuration.
Question 7: The oil red O stain requires frozen sections rather than paraffin sections because:
- Organic solvents used in paraffin processing dissolve lipids (Correct answer)
- Paraffin sections are too thick for lipid staining
- Oil red O does not adhere to paraffin-embedded tissue
- Formalin fixation destroys lipid antigens
Correct answer: Organic solvents used in paraffin processing dissolve lipids
Lipids are extracted by the xylene and alcohols used during paraffin embedding and processing, so frozen sections must be used to preserve them for oil red O staining.
HT Routine & Special Staining Methods 2
In the Periodic Acid-Schiff (PAS) reaction, periodic acid acts by: