Overview
Periodic acid–Schiff (PAS) staining is a widely used histochemical technique that highlights structures containing carbohydrates, including glycogen, mucoproteins, polysaccharides, and fungal cell wall components. According to the document, PAS works through a reaction where periodic acid oxidizes carbon–carbon bonds to produce aldehydes, which then react with fuchsin–sulfurous acid to form the characteristic magenta color (page 3).
PAS has a high affinity for glycogen, particularly in tissues such as hematopoietic cells (page 2). It is routinely used in histology, hematology, mycology, gastrointestinal pathology, kidney disease evaluation, carcinoma diagnosis, and metabolic disorder assessments (pages 4, 10–12). Its broad clinical value makes PAS one of the most fundamental staining techniques in diagnostic pathology.
Symptoms
Since PAS is a diagnostic stain rather than a clinical condition, the “symptoms” relate to the tissue abnormalities or diseases that prompt PAS staining, as shown across multiple pages.
1. Glycogen Storage Disorders
When glycogen accumulates abnormally in tissues—especially the liver or muscle—PAS helps visualize deposits (page 4). Clinical indicators leading to PAS testing may include hepatomegaly, hypoglycemia, or unexplained muscle weakness.
2. Leukemia-Related Changes
The document notes that ALL blasts show strong PAS positivity, while AML, AMML, and AMoL blasts typically do not (page 2). Symptoms that may lead to PAS use include fatigue, bruising, recurrent infections, or abnormal blood counts.
3. Fungal Infections
PAS highlights fungal hyphae that contain polysaccharides, appearing bright red (page 8). Symptoms prompting evaluation include persistent cough, fever, sinus infection, or chronic skin lesions.
4. Gastrointestinal and Renal Disorders
PAS detects neutral mucins, basement membrane changes, and proteinaceous deposits, often associated with diarrhea, malabsorption, nephrotic syndrome, or glomerular diseases (pages 10–11).
5. Alpha-1 Antitrypsin Deficiency
PAS-positive, diastase-resistant globules in hepatocytes indicate this condition (page 9), often accompanied by jaundice, liver dysfunction, or neonatal cholestasis.
Thus, PAS is ordered when underlying tissue abnormalities present with key clinical symptoms requiring microscopic clarification.
Causes
PAS staining positivity is caused by specific biochemical features within tissues. The document outlines several major causes:
1. Carbohydrate-Rich Structures
PAS highlights structures containing glycogen, mucoproteins, and polysaccharides. Causes include:
- Glycogen accumulation in storage diseases
- Basement membrane thickening
- Mucin-rich epithelial tissues
2. Fungal Cell Walls
Fungi such as Candida, Aspergillus, and Cryptococcus contain PAS-positive polysaccharides (page 10–11).
3. Diastase-Resistant Material
PAS combined with diastase digestion helps distinguish glycogen from α1-AT globules (page 9). PAS-positive diastase-resistant inclusions signify:
- Alpha-1 antitrypsin deficiency
- Mucinous carcinomas
- Polyglucosan body disease (page 12)
4. Structural Changes in Organs
Organ-specific causes demonstrated in the document include:
- Kidney glomerular abnormalities
- GI tract mucin alterations
- Pulmonary alveolar proteinosis (page 11)
These causes guide clinicians toward targeted diagnoses based on PAS staining patterns.
Risk Factors
Risk factors refer both to conditions that increase the likelihood of PAS-positive findings and technical limitations that may affect staining accuracy.
1. Diseases with High Carbohydrate Content
Tumors, infections, and metabolic diseases rich in glycogen or mucins show strong PAS positivity.
2. Leukemia Types
ALL blasts frequently test positive, so patients suspected of ALL are at higher likelihood of PAS use.
3. Alpha-1 Antitrypsin Deficiency & Liver Disorders
The presence of PAS-positive, diastase-resistant inclusions is a key diagnostic marker (page 9).
4. Technical Limitations in Staining
The limitations on page 13 list important risk factors for misinterpretation:
- Limited specificity (cannot differentiate carbohydrate types)
- Variable sensitivity due to tissue fixation
- Artifacts caused by formalin pigment
- Subjectivity between observers
- No quantification ability
- Need for control staining
5. Poor Sample Preparation
Inadequate paraffin embedding or poorly fixed blood smears (page 5) may compromise diagnostic accuracy.
Prevention
Prevention strategies focus on improving staining reliability and avoiding diagnostic errors.
1. Proper Sample Collection & Fixation
Use 10% formalin-fixed paraffin blocks and correctly prepared bone marrow or blood smears (page 5).
2. Accurate Reagent Preparation
The document details exact formulations for Schiff reagent, periodic acid, and Mayer’s hematoxylin (page 6). Proper preparation prevents false staining.
3. Controlled Staining Technique
Following each step—oxidation, Schiff reaction, washing, counterstaining, hydration, and clearing—ensures optimal staining (page 7).
4. Use of PAS–Diastase When Needed
Using diastase helps differentiate glycogen from diastase-resistant inclusions (page 9), preventing misdiagnosis.
5. Employing Experienced Personnel
Due to subjectivity (page 13), expert interpretation reduces variability and increases diagnostic reliability.
6. Including Control Slides
Control staining is essential to verify that PAS reactions are functioning correctly
