Periodic acid–Schiff stain

Ortho-Periodsäure

Gastric signet ring cell carcinoma histopatholgy (2) PAS stain

Esophageal candidiasis (2) PAS stain

Liver biopsy of glycogen storage disorder PAS positive

Periodic acid–Schiff stain (PAS) is a histochemical staining method used in anatomy, biochemistry, and pathology to detect polysaccharides such as glycogen, and mucosubstances such as glycoproteins, mucins, and mucopolysaccharides in tissues. The PAS stain is widely used to demonstrate fungal organisms in tissue sections and to highlight the basement membranes, making it a critical tool in the diagnosis of various diseases and conditions.

Principle

The PAS reaction involves the oxidation of the aldehyde groups present in the polysaccharides by periodic acid to form aldehydes, which then react with the Schiff reagent, resulting in a magenta or purple color. This reaction is specific to components containing a high proportion of carbohydrate material, especially those with vicinal diol groups that can be oxidized to aldehydes.

Procedure

The standard PAS staining procedure involves several steps:

1. Tissue sections are fixed, typically with formalin.
2. The sections are then treated with periodic acid, which oxidizes the diol groups to aldehydes.
3. After washing, the sections are treated with Schiff reagent, leading to the formation of a magenta color in areas where aldehydes are present.
4. The sections are then counterstained, often with hematoxylin, to visualize the nuclei and other tissue components not highlighted by PAS.

Applications

PAS staining has a broad range of applications in both clinical and research settings:

• In pathology, it is used to identify glycogen in liver diseases, diagnose fungal infections, and highlight the thickened basement membrane in diseases such as Alport syndrome and diabetic nephropathy.
• In dermatology, PAS staining helps in diagnosing skin diseases by highlighting the basement membrane zone.
• It is also used in the identification of glycogen storage diseases and to differentiate between various types of glomerulonephritis by demonstrating the distribution and deposition of glycogen and mucopolysaccharides.

Advantages and Limitations

The main advantage of PAS staining is its ability to selectively highlight components rich in carbohydrates, making it invaluable in the diagnosis and study of a wide range of diseases. However, its specificity can sometimes be a limitation, as not all pathologic entities can be identified with PAS staining alone. Interpretation of PAS-stained sections requires expertise in histology and pathology, as the staining pattern needs to be correlated with clinical and other histological findings.

See Also

• Histochemistry
• Glycogen storage disease
• Fungal infection
• Basement membrane

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