[Durgical](https://durgical.com/en/) › [DurgiPedia](https://durgical.com/en/durgipedia/) › [Histology](https://durgical.com/en/histology/) › [Methods and stains](https://durgical.com/en/histology/#a-methods) › From biopsy to slide: fixation, sectioning, frozen section

[Histology](https://durgical.com/en/histology/) · [Methods and stains](https://durgical.com/en/histology/#a-methods)

# From biopsy to slide: fixation, sectioning, frozen section

- Technique

Before tissue can be seen under a microscope it must be preserved, hardened, cut very thin and stained.

Updated 2026-11-01

**See it in 3D:** [Skin](https://durgical.com/en/anatomy/skin/) · [Liver](https://durgical.com/en/anatomy/liver/) · [Thyroid gland](https://durgical.com/en/anatomy/thyroid-gland/)

## Key points

- Order: fix, dehydrate, clear, embed in paraffin, cut, stain.
- Formalin cross-links proteins; glutaraldehyde is preferred for electron microscopy.
- Frozen = fast (minutes), less detail, keeps lipids; paraffin = days, best detail.
- Empty spaces in a routine section are usually dissolved lipid or mucin, not air.

## What it is

Histological processing turns a soft, perishable sample into thin, stable slides. Routine processing uses formalin fixation and paraffin embedding and gives the best detail but takes days; a frozen section gives an answer within minutes during surgery, with less detail.

## Step by step

- The sample (biopsy or surgical specimen) is taken and sent quickly to the lab to avoid autolysis.
- Fixation, almost always in buffered formalin: it cross-links proteins and stops self-digestion.
- Dehydration through increasing concentrations of alcohol.
- Clearing with a solvent (xylene) that mixes with paraffin.
- Embedding in molten paraffin to form a block that can be cut.
- Cutting on a microtome into sections a few micrometres thick, mounted on a glass slide.
- Dewaxing, staining (H&E or others) and coverslipping for the pathologist to read.

## Paraffin section versus frozen section

| Feature | Paraffin (permanent) | Frozen (intraoperative) |
| --- | --- | --- |
| Time | Several days | About 15 to 20 minutes |
| Instrument | Microtome | Cryostat |
| Detail | Best; the basis of the final diagnosis | Lower; ice-crystal artefacts |
| Lipids | Dissolved (fat cells look empty) | Preserved (useful for fat stains) |
| Typical use | Final diagnosis, immunohistochemistry, archive | Surgical margins, deciding the extent of surgery, immunofluorescence |

## Clinical notes

- A frozen section tells the surgeon in theatre whether a margin is free of tumour or a lymph node holds a metastasis.
- Late or poor fixation damages morphology and can distort immunohistochemistry (for example hormone receptors in breast cancer).
- Skin biopsies for suspected autoimmune blistering disease are also sent without formalin for direct immunofluorescence.

## Memory aid

Fix, dry, clear, wax, slice, dye: six verbs carry tissue from the operating table to the slide.

## Test yourself

Think of the answer, then tap the question to see it.

## What is the main job of formalin in tissue processing?

To fix the tissue: it cross-links proteins, stops autolysis and preserves the architecture.

## What is a frozen section used for during surgery?

To give a rapid diagnosis, for example whether a surgical margin is involved, in about 15 to 20 minutes.

## Why do fat cells look like empty spaces in a paraffin section?

The alcohols and xylene used in processing dissolve the lipid, leaving only the membrane and the pushed-aside nucleus.

[Add to my cards (3)](https://durgical.app/estudiar/?add=/en/histology/from-biopsy-to-slide-fixation-sectioning-frozen-section/)

## See it in 3D

The structures of Durgical's 3D anatomy where it is found.

- [Skin](https://durgical.com/en/anatomy/skin/)
- [Liver](https://durgical.com/en/anatomy/liver/)
- [Thyroid gland](https://durgical.com/en/anatomy/thyroid-gland/)

## Related

- [Microscopy and stains: H&E, PAS, trichrome, silver, immunohistochemistry](https://durgical.com/en/histology/microscopy-and-stains-h-y-e-pas-trichrome-silver-immunohistochemistry/)
- [Electron microscopy: what it shows that light can't](https://durgical.com/en/histology/electron-microscopy-what-it-shows-that-light-can-t/)
- [Adipose tissue: white and brown fat](https://durgical.com/en/histology/adipose-tissue-white-and-brown-fat/)

## Related conditions

- [Breast cancer](https://durgical.com/en/conditions/breast-cancer/)
- [Thyroid cancer (papillary)](https://durgical.com/en/conditions/thyroid-cancer/)

[← All of histology](https://durgical.com/en/histology/)

Educational content on normal microscopic structure and its clinical relevance; no substitute for studying slides or for a health professional's advice.

Sources: [Tissue preparation 1](https://digitalhistology.org/histology-basics/tissue-preparation/tissue-1/) (Digital Histology, 2024); [Pathology Reports](https://www.cancer.gov/about-cancer/diagnosis-staging/diagnosis/pathology-reports-fact-sheet) (National Cancer Institute, 2024).

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Representative model, for educational purposes only.

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Source: https://durgical.com/en/histology/from-biopsy-to-slide-fixation-sectioning-frozen-section/
License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/histology/from-biopsy-to-slide-fixation-sectioning-frozen-section/