Toluidine Blue
Definition
A nuclear dye applied to anogenital skin that is taken up by nucleated cells exposed by micro-lacerations. It stains micro-tears dark blue, making them visible colposcopically when direct illumination alone would miss them.
- Type
- Nuclear dye
- Applied to
- Anogenital skin
- Target
- Nucleated cells exposed by micro-lacerations
- Result
- Micro-tears stain dark blue, visible on colposcopy
Common questions
Why does toluidine blue reveal micro-lacerations that are otherwise invisible?+
The dye binds nuclear material, which is normally protected under intact skin surface layers. A micro-laceration exposes deeper nucleated cells at the wound edge, so the dye takes up selectively there and stains only the injury, not the surrounding intact skin.
Does a negative toluidine blue result rule out anogenital injury?+
No. Absence of staining does not exclude an assault, since injuries can heal within days, may not break the epithelium enough to expose nucleated cells, or may be located outside the area examined, so a negative test is interpreted alongside history and other findings.
How is toluidine blue used differently from plain colposcopic photography?+
Colposcopy alone provides magnification and light but relies on visible contrast to spot injury, while toluidine blue adds a chemical stain step that increases the visibility of micro-tears specifically, so the two are typically used together rather than as alternatives.
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