PAS stain

The Periodic acid–Schiff stain (PAS stain) is a histological staining technique used to detect polysaccharides such as glycogen, mucosubstances like glycoproteins, glycolipids, and mucins in tissues. It is widely used in medical diagnostics and research to highlight structures in tissue sections.

Principle

The PAS stain is based on the oxidation of certain tissue elements by periodic acid, which converts 1,2-glycols into aldehydes. These aldehydes then react with the Schiff reagent, a fuchsin-sulfurous acid compound, to produce a magenta or purple color. This reaction is specific for polysaccharides and related substances, making it a valuable tool for identifying these components in tissue samples.

Applications

The PAS stain is used in various applications, including:

• Glycogen detection: It is used to identify glycogen storage diseases by highlighting glycogen deposits in tissues.
• Fungal infections: PAS stain is effective in identifying fungi in tissue sections, as the fungal cell wall contains polysaccharides that react with the stain.
• Basement membrane visualization: It is used to visualize basement membranes in kidney biopsies, aiding in the diagnosis of glomerular diseases.
• Mucin detection: PAS stain can highlight mucin in epithelial tissues, which is useful in diagnosing certain types of adenocarcinomas.

Procedure

The PAS staining procedure involves several steps:

1. Fixation: Tissue samples are fixed in formalin to preserve cellular structures.
2. Oxidation: The tissue is treated with periodic acid, which oxidizes the 1,2-glycol groups to aldehydes.
3. Schiff reagent application: The tissue is then exposed to the Schiff reagent, which reacts with the aldehydes to produce a magenta color.
4. Counterstaining: A counterstain, such as hematoxylin, may be applied to provide contrast and highlight cellular details.

Interpretation

The PAS stain results in a magenta coloration of structures containing polysaccharides. The intensity of the staining can provide information about the quantity and distribution of these substances within the tissue. Pathologists interpret these patterns to diagnose various conditions.

Limitations

While the PAS stain is highly specific for polysaccharides, it does not differentiate between different types of polysaccharides. Additional stains or techniques may be required to further characterize the substances present in the tissue.

Also see

• Hematoxylin and eosin stain
• Masson's trichrome stain
• Silver stain
• Glycogen storage disease
• Histology