Kastle-Meyer Test
Definition
Phenolphthalein based presumptive test. Reduced phenolphthalin is oxidised by haem peroxidase activity in the presence of hydrogen peroxide to give a pink colour. Sensitivity around 1 in 10,000 to 1 in 100,000 dilutions.
- Chemistry
- Phenolphthalin oxidised to phenolphthalein by haem peroxidase
- Sensitivity
- Detects blood diluted about 1 in 10,000 to 1 in 100,000
- Positive result
- Pink colour
- Reliability class
- Presumptive screening test only
Common questions
What can produce a false positive on this test?+
Non-blood peroxidases in potatoes, horseradish, and some other plant material, along with certain metal ions and household bleaches, can catalyse the same colour reaction, which is why a positive must be followed by a species-specific confirmatory test.
How does its sensitivity compare with other presumptive blood tests?+
Its detection range of roughly 1 in 10,000 to 1 in 100,000 dilution is comparable to phenolphthalein-based tests generally and is sensitive enough for most casework stains, though luminol offers greater sensitivity for very faint or cleaned-up bloodstains.
Does a positive result identify the species the blood came from?+
No. The reaction only detects peroxidase-like activity consistent with haemoglobin, so species origin still requires a separate confirmatory method such as an anti-human haemoglobin immunoassay.
Related terms
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- Confirmatory Test
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- Leucomalachite Green (LMG)
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- Luminol
- A chemiluminescent reagent (5-amino-2,3-dihydro-1,4-phthalazinedione) that produces blue-white light on contact with haemoglobin-derived iron. Detects blood diluted to 1:10,000,000 or more. Used as...
- Presumptive Test
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- Takayama Test
- Confirmatory crystal test. Pyridine, glucose and sodium hydroxide convert haem to pink, feathery pyridine ferroprotoporphyrin (haemochromogen) crystals.
- Teichmann Test
- Confirmatory crystal test. Glacial acetic acid and sodium chloride convert haem to brown, rhombic haemin (ferriprotoporphyrin chloride) crystals. Older, less reliable on...