Knowledge Base › Troubleshooting Atlas › Special stains
PAS stain weak or negative
Also known as: Periodic Acid-Schiff
What it looks like
Tissue sections show weak or no staining of glycogen and mucopolysaccharides. Positive controls may appear pale or unstained.
Where it usually appears: Commonly used in liver, kidney, and fungal tissue sections.
Likely causes
- Insufficient fixation time
- Inadequate reagent concentration
- Expired or improperly stored reagents
- Inaccurate timing during staining process
- Poor tissue processing
Immediate checks
- Verify reagent expiration dates
- Check fixation duration and quality
- Inspect for proper tissue processing
Corrective action
- Re-fix tissue samples if necessary
- Prepare fresh reagents or adjust concentrations
- Re-stain with proper timing adjustments
Preventive action
- Regularly calibrate and maintain equipment
- Ensure proper training for staff on staining protocols
- Store reagents according to manufacturer guidelines
This atlas is for educational purposes for laboratory professionals. It does not replace your institutional SOPs, manufacturer instructions, validated protocols or pathologist judgment. Adapt any action to your laboratory and equipment.
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