Why are frozen sections stained for fat with Oil Red O mounted in an aqueous mountant?

Xylene would dissolve the lipid

Fat stains need an acidic mountant

Resin mountants bleach the red dye

A laboratory changes from Harris hematoxylin used regressively to Mayer's hematoxylin used progressively for H&E. Which step should be removed from the schedule?

Differentiation in acid alcohol

In the indirect (two-step) immunoperoxidase method, the enzyme label is attached to:

A secondary antibody against the primary

The tissue antigen before staining

The chromogen before it is applied

The primary antibody against the antigen

Histotechnology: staining, mounting and IHC

22 Kerala PSC Lab Technician Gr II practice questions on Histotechnology: staining, mounting and IHC, part of Pathology. The first 22 are below; the first 5 with answers and explanations (tap Show answer after you have chosen), the rest in Learn with a free account.

Question 1 · Easy
DPX, the usual mountant for H&E sections, is a resin dissolved in:
1. AWater
2. BXylene
3. CGlycerol
4. DEthanol
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Answer: B · Xylene
DPX is distrene (a polystyrene), a plasticizer (dibutyl phthalate) and xylene. Because it mixes with xylene, sections go straight from the last xylene into DPX under the coverslip. It dries hard and colorless with a refractive index close to glass, and keeps stains for years. Any water left in the section makes the mount cloudy.
- A: Water-based mountants such as glycerine jelly are used for fat stains.
- C: Glycerol is the base of aqueous mountants, not of DPX.
- D: Ethanol is used for dehydration; slides go into DPX from xylene, not alcohol.
Question 2 · Medium
Why are frozen sections stained for fat with Oil Red O mounted in an aqueous mountant?
1. AAqueous mountants set harder
2. BFat stains need an acidic mountant
3. CXylene would dissolve the lipid
4. DResin mountants bleach the red dye
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Answer: C · Xylene would dissolve the lipid
Mounting in a resin such as DPX first needs dehydration in alcohol and clearing in xylene, and both dissolve lipids. Fat stains such as Oil Red O and Sudan dyes are therefore done on frozen sections and mounted straight from water in glycerine jelly or another aqueous mountant. These mounts stay soft, so the coverslip edges may be sealed with varnish. The same reason explains why fat is absent from paraffin sections.
- A: Aqueous mountants are softer than DPX and may need sealing with varnish.
- B: Glycerine jelly is chosen because it is water-based, not for its pH.
- D: The problem is the solvents a resin mount needs, not bleaching of the dye.
Question 3 · Hard
A laboratory changes from Harris hematoxylin used regressively to Mayer's hematoxylin used progressively for H&E. Which step should be removed from the schedule?
1. ADifferentiation in acid alcohol
2. BBluing in Scott's tap water
3. CCounterstaining in eosin
4. DClearing in xylene
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Answer: A · Differentiation in acid alcohol
In a progressive method the nuclei are stained only to the end point and the stain is then stopped, so nothing has to be removed. The acid alcohol step, which takes excess dye out of a deliberately overstained section in the regressive method, is therefore left out. Bluing is still needed, because alum hematoxylin stays red until it is turned blue in alkaline conditions. Staining time becomes critical, so it is checked against a control slide.
- B: All alum hematoxylins need bluing to turn the nuclei blue.
- C: Eosin is still needed to stain the cytoplasm.
- D: Sections must still be cleared before resin mounting.
Question 4 · Easy
What color do glycogen and other positive materials give in the periodic acid-Schiff (PAS) reaction?
1. ABlack
2. BBrown
3. CBlue
4. DMagenta
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Answer: D · Magenta
Periodic acid oxidizes 1,2-glycol groups to aldehydes, which react with Schiff reagent to give a magenta color. Glycogen, neutral mucins, basement membranes and fungal walls are PAS positive. Digestion with diastase before the stain removes glycogen but not the others. Nuclei are counterstained blue with hematoxylin.
- A: Black is the color of reticulin fibers in a silver stain.
- B: Brown is the DAB product in immunoperoxidase staining.
- C: Blue is the Prussian blue of iron in the Perls stain.
Question 5 · Medium
In the indirect (two-step) immunoperoxidase method, the enzyme label is attached to:
1. AThe tissue antigen before staining
2. BA secondary antibody against the primary
3. CThe chromogen before it is applied
4. DThe primary antibody against the antigen
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Answer: B · A secondary antibody against the primary
In the indirect method an unlabeled primary antibody binds the tissue antigen. An enzyme-labeled secondary antibody, raised against immunoglobulin of the primary antibody's species, then binds the primary. Several secondary molecules can bind each primary, which amplifies the signal, and one labeled secondary serves many primaries. The enzyme (peroxidase) then converts DAB to a brown product at the antigen site.
- A: The antigen is never labeled; the antibody detects it.
- C: The chromogen is the enzyme's substrate, not a carrier of the label.
- D: A labeled primary antibody is the direct method.
Question 6 · Easy
In Perls' Prussian blue stain, ferric iron in hemosiderin reacts with acidified:
1. APotassium ferrocyanide
2. BPeriodic acid
3. CPotassium ferricyanide
4. DSilver nitrate
Answer and explanation in LearnFree account
Question 7 · Medium
Why are formalin-fixed paraffin sections heated in citrate buffer (pH 6) before many immunostains?
1. ATo unmask antigens hidden by cross-links
2. BTo make the sections stick to the glass slide
3. CTo block the tissue's own peroxidase
4. DTo remove the wax from the sections
Answer and explanation in LearnFree account
Question 8 · Easy
Gordon and Sweet's method is used in histology to demonstrate:
1. AReticulin fibers
2. BGlycogen
3. CHemosiderin
4. DAcid-fast bacilli
Answer and explanation in LearnFree account
Question 9 · Medium
In H&E staining, eosin colors the cytoplasm because eosin is:
1. AA basic dye that binds nuclear nucleic acids
2. BAn acidic dye that binds basic proteins
3. CA lipid-soluble dye that enters fat
4. DA metal lake bound through a mordant
Answer and explanation in LearnFree account
Question 10 · Hard
In an immunoperoxidase run on a bone marrow trephine, both the test section and its negative control (primary antibody left out) show brown deposits in red cells and granulocytes. The most likely error is:
1. AHydrogen peroxide block was left out
2. BThe counterstain was left too long
3. CThe primary antibody was too dilute
4. DAntigen retrieval was too short
Answer and explanation in LearnFree account
Question 11 · Medium
A poorly differentiated tumor stains strongly positive for cytokeratin and negative for CD45 and S-100 by immunohistochemistry. This profile suggests:
1. ALymphoma
2. BCarcinoma
3. CSarcoma
4. DMelanoma
Answer and explanation in LearnFree account
Question 12 · Medium
A Perls' stain on a bone marrow aspirate from an anemic woman shows no blue granules in the marrow fragments, while the control is positive. This finding indicates:
1. AAnemia of chronic disease
2. BIron deficiency
3. CIron overload
4. DSideroblastic anemia
Answer and explanation in LearnFree account
Question 13 · Medium
Why is a known positive control section stained with every immunohistochemistry run?
1. ATo measure the section thickness
2. BTo reduce the cost of antibody
3. CTo show a negative test is a true negative
4. DTo block the tissue's own peroxidase
Answer and explanation in LearnFree account
Question 14 · Hard
A lung biopsy from a 45-year-old man shows caseating granulomas. The Ziehl-Neelsen stain shows no acid-fast bacilli, and the known positive control slide stained alongside it is also negative. What should the laboratory do?
1. AReport a fungal infection instead
2. BRepeat the stain with fresh reagents
3. CReport the biopsy as negative for AFB
4. DStain the section by PAS only
Answer and explanation in LearnFree account
Question 15 · Medium
For Mycobacterium leprae in skin biopsies, the Fite-Faraco method is preferred to the routine Ziehl-Neelsen stain because:
1. AM. leprae loses its color in strong acid-alcohol
2. BM. leprae does not take up carbol fuchsin
3. CM. leprae stains only with fluorescent dyes
4. DM. leprae is destroyed by heat fixation
Answer and explanation in LearnFree account
Question 16 · Easy
The von Kossa method is used to demonstrate:
1. AFerric iron
2. BMelanin
3. CGlycogen
4. DCalcium deposits
Answer and explanation in LearnFree account
Question 17 · Easy
A renal biopsy from a patient with suspected amyloidosis is stained routinely with:
1. AAlcian blue
2. BMasson-Fontana
3. COil Red O
4. DCongo red
Answer and explanation in LearnFree account
Question 18 · Easy
In the classic Harris hematoxylin formula, the hematoxylin is ripened with:
1. AMercuric oxide
2. BHydrogen peroxide
3. CSodium iodate
4. DPotassium permanganate
Answer and explanation in LearnFree account
Question 19 · Medium
Why must paraffin sections be dewaxed in xylene and taken through alcohols to water before H&E staining?
1. AAlcohol makes the nuclei basophilic
2. BWater is needed to soften the section
3. CXylene fixes the tissue again
4. DAqueous dyes cannot penetrate wax
Answer and explanation in LearnFree account
Question 20 · Easy
In Van Gieson's stain, collagen fibers are stained:
1. AYellow
2. BBlack
3. CRed
4. DBlue
Answer and explanation in LearnFree account
Question 21 · Hard
H&E sections from a run show irregular pale, unstained patches where neither hematoxylin nor eosin has taken, while the rest of each section is well stained. The xylene in the first dewaxing jar has not been changed for weeks. What is the cause?
1. AInadequate bluing after hematoxylin
2. BExhausted eosin solution
3. CIncomplete removal of wax
4. DOver-differentiation in acid alcohol
Answer and explanation in LearnFree account
Question 22 · Easy
Which of these is an aqueous mountant?
1. APermount
2. BGlycerine jelly
3. CDPX
4. DCanada balsam
Answer and explanation in LearnFree account

Histotechnology: staining, mounting and IHC

DPX, the usual mountant for H&E sections, is a resin dissolved in:

Why are frozen sections stained for fat with Oil Red O mounted in an aqueous mountant?

A laboratory changes from Harris hematoxylin used regressively to Mayer's hematoxylin used progressively for H&E. Which step should be removed from the schedule?

What color do glycogen and other positive materials give in the periodic acid-Schiff (PAS) reaction?

In the indirect (two-step) immunoperoxidase method, the enzyme label is attached to:

In Perls' Prussian blue stain, ferric iron in hemosiderin reacts with acidified:

Why are formalin-fixed paraffin sections heated in citrate buffer (pH 6) before many immunostains?

Gordon and Sweet's method is used in histology to demonstrate:

In H&E staining, eosin colors the cytoplasm because eosin is:

In an immunoperoxidase run on a bone marrow trephine, both the test section and its negative control (primary antibody left out) show brown deposits in red cells and granulocytes. The most likely error is:

A poorly differentiated tumor stains strongly positive for cytokeratin and negative for CD45 and S-100 by immunohistochemistry. This profile suggests:

A Perls' stain on a bone marrow aspirate from an anemic woman shows no blue granules in the marrow fragments, while the control is positive. This finding indicates:

Why is a known positive control section stained with every immunohistochemistry run?

A lung biopsy from a 45-year-old man shows caseating granulomas. The Ziehl-Neelsen stain shows no acid-fast bacilli, and the known positive control slide stained alongside it is also negative. What should the laboratory do?

For Mycobacterium leprae in skin biopsies, the Fite-Faraco method is preferred to the routine Ziehl-Neelsen stain because:

The von Kossa method is used to demonstrate:

A renal biopsy from a patient with suspected amyloidosis is stained routinely with:

In the classic Harris hematoxylin formula, the hematoxylin is ripened with:

Why must paraffin sections be dewaxed in xylene and taken through alcohols to water before H&E staining?

In Van Gieson's stain, collagen fibers are stained:

H&E sections from a run show irregular pale, unstained patches where neither hematoxylin nor eosin has taken, while the rest of each section is well stained. The xylene in the first dewaxing jar has not been changed for weeks. What is the cause?

Which of these is an aqueous mountant?