Knowledge Base › Troubleshooting Atlas › Special stains
Ziehl-Neelsen (AFB) weak or false-negative
Also known as: AFB stain
What it looks like
Acid-fast bacilli appear as bright red rods against a blue or green background.
Where it usually appears: Typically seen in tissue sections suspected of containing mycobacterial infections.
Likely causes
- Insufficient decolorization time
- Inadequate staining time
- Expired reagents
- Improper fixation of tissue
- Low concentration of mycobacteria in sample
Immediate checks
- Verify staining protocol adherence
- Check reagent expiration dates
- Inspect tissue fixation quality
Corrective action
- Repeat the staining procedure with adjusted times
- Ensure proper tissue processing and embedding
- Use fresh reagents
Preventive action
- Regularly calibrate and maintain equipment
- Train staff on proper staining techniques
- Perform routine quality control on stains
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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