Periodic Acid-Schiff (PAS) Reaction
Definition
A histochemical staining method that oxidises polysaccharides (including glycogen) to produce aldehydes, which are then detected by Schiff reagent as a magenta colour. Used to detect glycogen-rich vaginal epithelial cells in smear preparations.
- Chemistry
- Oxidises polysaccharides to aldehydes
- Detection reagent
- Schiff reagent
- Colour result
- Magenta
- Forensic use
- Detecting glycogen-rich vaginal epithelial cells
Common questions
Why is glycogen content useful for identifying vaginal epithelial cells specifically?+
Vaginal epithelial cells are notably glycogen-rich compared with most other cell types found in forensic samples, so a strong PAS-positive magenta reaction helps distinguish them from other cell types present on a slide or swab.
Does a positive PAS reaction alone confirm vaginal origin?+
No, other glycogen-containing cells can also stain positive, so examiners combine PAS staining with cell morphology and case context rather than relying on colour reaction alone to identify vaginal fluid.
Can degraded or aged samples still give a reliable PAS result?+
Glycogen can break down over time or with bacterial activity, so older or poorly preserved samples may give a weaker or negative reaction even when vaginal cells were originally present, which examiners factor into interpretation.
Related terms
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- Glycogen
- A polysaccharide energy store present in vaginal epithelial cells. It is released when cells are lysed and can be detected by periodic...
- RSID-Vaginal Mucosa
- Rapid Stain Identification of Vaginal Mucosa. An immunochromatographic lateral-flow assay using antibodies targeting proteins specific to human vaginal epithelial cells, providing higher...
- Urobilinogen
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