Periodic Acid-Schiff (PAS) Stain Test
Periodic Acid-Schiff (PAS) Stain Test
The Periodic Acid-Schiff (PAS) Stain is a histochemical staining technique used to detect polysaccharides, glycoproteins, mucins, and fungal organisms in tissues and cells. It is widely used in pathology and microbiology to diagnose a variety of gastrointestinal, renal, hematologic, and infectious diseases.
The PAS stain works by oxidizing glycogen and other carbohydrate-rich structures using periodic acid, producing aldehydes that react with Schiff’s reagent to create a red or magenta color. This reaction highlights fungi, basement membranes, glycogen deposits, and mucins, making it an essential diagnostic tool in renal diseases, blood disorders, and infections.
What is the PAS Stain Used For?
This stain is used to:
- Identify fungal infections (e.g., Candida, Histoplasma, Cryptococcus).
- Detect glycogen storage diseases in liver and muscle tissues.
- Highlight basement membrane abnormalities in kidney diseases.
- Identify mucin-producing tumors in the gastrointestinal tract.
- Diagnose certain hematologic disorders, such as acute lymphoblastic leukemia (ALL).
Procedure for PAS Staining
During tissue sample preparation, a thin tissue section is fixed on a slide, and oxidised with periodic acid to converts carbohydrates into aldehydes. Then the Schiff’s Reagent is applied, which reacts with aldehydes to form a red/magenta stain. Counterstaining is another option where Hematoxylin may be used for better contrast. The stained structures are then examined under a microscope.
Interpretation of Results
- PAS Positive (Magenta/Red Staining)- Indicates the presence of glycogen, fungal elements, mucins, or basement membranes.
- PAS Negative (No Staining)- Suggests absence of polysaccharides or related structures.
FAQs
Why is PAS staining important in fungal infections?
PAS highlights fungal cell walls, helping in the diagnosis of Candida, Histoplasma, and Cryptococcus infections.
How does PAS staining help in kidney disease diagnosis?
It detects thickened basement membranes and glycogen deposits, useful in diabetic nephropathy and glomerulonephritis.
What is the difference between PAS and PAS-D (diastase digestion)?
PAS-D removes glycogen, distinguishing glycogen-rich tissues from mucins and fungal elements.
Is PAS staining used in cancer diagnosis?
Yes, it helps identify mucin-producing tumors in the gastrointestinal and respiratory tracts.
Can PAS staining be used in blood disorders?
Yes, it is valuable in diagnosing acute lymphoblastic leukemia (ALL), where PAS-positive blasts are seen.
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