OSPE Station Name

Station 7 — Tissue Processing and H&E Staining

By the end of this station, the student should be able to:

1. Describe the basic steps of tissue processing for histopathology.
2. Perform or demonstrate the main supervised steps of H&E staining and identify the expected staining result.

Required Material

• Tissue specimen
• 10% formalin fixative
• Tissue cassette
• Alcohol grades for dehydration
• Xylene or clearing agent
• Paraffin wax
• Embedding mold
• Microtome section slide, already prepared if cutting is not required
• Glass slides
• Hematoxylin stain
• Eosin stain
• Distilled water
• Acid alcohol, if differentiation is included
• Ammonia water or alkaline water, if bluing is included
• DPX or mounting medium
• Coverslip
• Forceps
• Staining jars
• Gloves
• Lab coat
• Waste container

Student Task / Procedure

1. Wear lab coat and gloves.
2. Identify the tissue specimen and tissue cassette.
3. State the first step: fixation in 10% formalin.
4. Explain dehydration using ascending grades of alcohol.
5. Explain clearing using xylene.
6. Explain impregnation with molten paraffin wax.
7. Explain embedding of tissue in paraffin block.
8. Identify the prepared thin tissue section on a glass slide.
9. Deparaffinize the slide using xylene, if required.
10. Rehydrate the section through descending grades of alcohol to water.
11. Stain the section with hematoxylin.
12. Wash in water.
13. Differentiate and blue the section, if included in the lab protocol.
14. Counterstain with eosin.
15. Dehydrate through ascending grades of alcohol.
16. Clear in xylene.
17. Mount with DPX and coverslip.
18. Observe the stained slide under microscope.

Observation / Identification Points
The student should observe, identify, or demonstrate:

• Tissue is fixed before processing.
• Formalin preserves tissue architecture.
• Alcohol removes water from tissue.
• Xylene clears alcohol and makes tissue ready for wax.
• Paraffin supports tissue for thin section cutting.
• Thin sections are mounted on glass slides.
• Hematoxylin stains nuclei blue-purple.
• Eosin stains cytoplasm and extracellular matrix pink.
• Proper H&E slide shows clear nuclear and cytoplasmic contrast.
• Slide should be clean, properly mounted, and free from major folds, air bubbles, and excess stain.

Result / Interpretation

A properly processed and H&E-stained tissue section should show:

• Nuclei: blue-purple
• Cytoplasm: pink
• Muscle/collagen/extracellular matrix: pink shades
• Clear tissue architecture
• Good contrast between nucleus and cytoplasm

Principle:
Tissue processing converts soft biological tissue into a firm paraffin block so that thin sections can be cut. H&E staining uses hematoxylin as a basic nuclear stain and eosin as an acidic cytoplasmic stain.

Clinical Significance:
H&E staining is the routine basic stain used in histopathology. It helps identify normal tissue architecture, inflammation, necrosis, tumors, and other pathological changes.

Common Student Mistakes

1. Confusing dehydration with clearing.
2. Forgetting that fixation is the first essential step.
3. Saying eosin stains nuclei.
4. Saying hematoxylin stains cytoplasm.
5. Not knowing the correct color of nuclei and cytoplasm in H&E stain.
6. Skipping deparaffinization before staining.
7. Overstaining or understaining the section.
8. Not mounting the slide properly.
9. Producing air bubbles under coverslip.
10. Handling xylene/formalin without safety precautions.

AIM Feedback

Tissue processing should be remembered as a sequence: fixation → dehydration → clearing → impregnation → embedding → sectioning → staining → mounting. In H&E staining, the most exam-important point is color interpretation: hematoxylin stains nuclei blue-purple, while eosin stains cytoplasm and extracellular matrix pink. A good slide depends on proper processing, correct staining sequence, and clean mounting.

Most Important Viva Questions for This Topic

1. What is tissue processing?
   Tissue processing is the preparation of tissue for microscopic examination by fixation, dehydration, clearing, paraffin impregnation, embedding, sectioning, staining, and mounting.
2. What is the first step in tissue processing?
   Fixation.
3. Which fixative is commonly used in routine histopathology?
   10% formalin.
4. What is the purpose of fixation?
   It preserves tissue structure and prevents autolysis and putrefaction.
5. What is dehydration in tissue processing?
   Dehydration is the removal of water from tissue using ascending grades of alcohol.
6. Why is clearing done?
   Clearing removes alcohol and makes tissue compatible with paraffin wax.
7. Which clearing agent is commonly used?
   Xylene.
8. What is the purpose of paraffin embedding?
   Paraffin gives support to the tissue so thin sections can be cut.
9. Which instrument is used to cut thin tissue sections?
   Microtome.
10. What does hematoxylin stain?
    Hematoxylin stains nuclei blue-purple.
11. What does eosin stain?
    Eosin stains cytoplasm and extracellular matrix pink.
12. What is the clinical importance of H&E staining?
    It is the routine stain for studying tissue architecture and diagnosing many pathological conditions such as inflammation, necrosis, and tumors.