What is Formaldehyde?
Formaldehyde is a simple aldehyde with the chemical formula CH₂O. It is a colorless gas with a pungent odor and is highly soluble in water. In the context of
histology, formaldehyde is primarily used as a fixative to preserve biological tissues.
Why is Formaldehyde Used in Histology?
Formaldehyde is widely used in histology because it effectively cross-links proteins, which stabilizes the tissue structure and prevents autolysis and decay. This is essential for maintaining the tissue’s
morphology and integrity for microscopic examination.
How Does Formaldehyde Fix Tissue?
Formaldehyde forms covalent bonds with amino groups in proteins, creating a network of cross-links that immobilize the cellular structures. This process is known as
fixation. The most commonly used solution is 10% neutral buffered formalin, which contains 4% formaldehyde.
It provides excellent preservation of cellular and subcellular structures.
It is compatible with most staining techniques.
It allows for long-term storage of specimens.
It is toxic and a known
carcinogen, requiring careful handling and proper ventilation.
It can cause shrinkage and hardening of tissues if used improperly.
It can mask antigenic sites, complicating
immunohistochemistry.
Use in a well-ventilated area, preferably in a fume hood.
Wear appropriate personal protective equipment (PPE), including gloves, goggles, and lab coats.
Store formaldehyde solutions in tightly sealed containers to prevent vapor release.
How is Formaldehyde Neutralized?
Formaldehyde can be neutralized using chemicals like sodium bisulfite or by converting it into less hazardous compounds. Proper disposal procedures should be followed according to institutional and regulatory guidelines.
Alternatives to Formaldehyde
There are several alternatives to formaldehyde for tissue fixation, including: Glutaraldehyde: Provides superior cross-linking but is more toxic.
Alcohol-based fixatives: Faster penetration but may cause dehydration and shrinkage.
Zinc-based fixatives: Less toxic and suitable for antigen preservation.
