OVERVIEW:
STEPS IN TISSUE PROCESSING FOR PARAFFIN SECTIONS:
1. OBTAINING A FRESH SPECIMEN:
A fresh tissue sample can very easily be damaged during a surgical or non-surgical procedure. The sample must be handled carefully and appropriately fixed as soon as possible after the removal. Ideally, fixation should take place at the site of removal, preferably in the operating theatre.
2. FIXATION
The obtained specimen is then placed in a liquid fixing agent (fixative) such as a formaldehyde solution (formalin). This will slowly penetrate the tissue causing chemical and physical changes that will harden and preserve the tissue and protect it against subsequent processing steps
3. DEHYDRATION
As melted paraffin wax is hydrophobic , most of the water in a specimen must be removed before it can be infiltrated with wax. This process is commonly carried out by immersing specimens in a series of ethanol (alcohol) solutions of increasing concentration until pure, water-free alcohol is reached.
4. CLEARING
A clearing agent is used during this step. A popular clearing agent is xylene and multiple changes are required to completely displace ethanol.
5. WAX INFILTRATION
The tissue sample is now ready to be embedded with suitable histological wax.
6. EMBEDDING OR BLOCKING OUT
Now that the specimen is thoroughly infiltrated with wax it must be formed into a “block” which can be clamped into a microtome for section cutting.
