Laboratory investigations
- barium enema to test for cathartic colon - ahaustral right colon.
- sigmoidoscopy - may see melanosis coli (microscopic form is often the normal variant).
- alkalinisation of stool: phenolphthalein, some anthraquinones, and rhubarb turn red; bisacodyl turns purple-blue.
- thin-layer chromatography or spectrophotometry of urine or stool water: detects anthraquinones, bisacodyl, phenolphthalein
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