ASCP Special Stains and Histochemistry 1 — Questions and Answers
Question 1: What does the PAS (Periodic Acid-Schiff) stain primarily identify?
- Nuclei and DNA
- Glycogen, neutral mucins, and basement membranes (Correct answer)
- Elastic fibers
- Amyloid deposits
Correct answer: Glycogen, neutral mucins, and basement membranes
PAS stains 1,2-glycol groups in polysaccharides, glycoproteins, and mucins magenta-red by oxidizing them with periodic acid and then applying Schiff reagent.
Question 2: In a Masson's trichrome stain, what color does collagen appear?
- Red
- Blue or green (Correct answer)
- Yellow
- Black
Correct answer: Blue or green
Masson's trichrome stains collagen blue (or green in the Goldner variant), muscle red, and nuclei dark brown-black.
Question 3: Which special stain is used to identify iron (hemosiderin) deposits in tissue?
- Congo red
- Prussian blue (Perl's stain) (Correct answer)
- Oil Red O
- Alcian blue
Correct answer: Prussian blue (Perl's stain)
Perl's Prussian blue reacts ferric iron with potassium ferrocyanide to produce a bright blue precipitate at iron deposition sites.
Question 4: What is the characteristic staining result of amyloid with Congo red?
- Blue birefringence under polarized light
- Apple-green birefringence under polarized light (Correct answer)
- Red fluorescence only
- Negative staining
Correct answer: Apple-green birefringence under polarized light
Amyloid stained with Congo red shows salmon-pink color in brightfield and apple-green birefringence under polarized light.
Question 5: Which stain is used to identify fungi and mucin simultaneously in tissue sections?
- Masson's trichrome
- GMS (Grocott's methenamine silver)
- PAS (Periodic Acid-Schiff)
- Both GMS and PAS (Correct answer)
Correct answer: Both GMS and PAS
Both GMS and PAS are effective for identifying fungal organisms; GMS turns fungi black, while PAS stains them magenta.
Question 6: What is the purpose of using a diastase control with a PAS stain?
- To enhance mucin staining
- To confirm that PAS-positive material is glycogen by removing it with diastase pretreatment (Correct answer)
- To block non-specific background
- To differentiate neutral from acid mucins
Correct answer: To confirm that PAS-positive material is glycogen by removing it with diastase pretreatment
Diastase digests glycogen; if PAS positivity disappears after diastase treatment, the material was glycogen rather than other PAS-positive substances.
ASCP Special Stains and Histochemistry 1
What does the PAS (Periodic Acid-Schiff) stain primarily identify?