The Kastle-Meyer test is a common presumptive test used in forensic science to detect the presence of blood. It is based on the reaction between hemoglobin, a protein found in red blood cells, and a chemical called phenolphthalein. When phenolphthalein is mixed with hydrogen peroxide and comes into contact with blood, it produces a pink color due to the presence of hemoglobin.
The Kastle-Meyer test involves the following steps:
Collection of the sample: The suspected blood sample is collected from a surface, object, or clothing using a sterile swab.
Application of reagents: A few drops of phenolphthalein solution are applied to the swab, followed by a few drops of hydrogen peroxide solution.
Observation of color change: If blood is present in the sample, the mixture will turn pink within a few seconds, indicating a positive result. If no blood is present, the mixture will remain colorless.
The Kastle-Meyer test is a presumptive test, meaning that it does not definitively identify the presence of blood, but rather indicates the likelihood of its presence. Further confirmatory testing, such as DNA analysis or serological testing, is necessary to confirm the presence of blood and to identify its source.
The Kastle-Meyer test is a relatively simple and quick test to perform, and is commonly used by law enforcement and forensic investigators in the field as a first step in identifying potential blood evidence. However, it is important to note that the test can produce false positives, as other substances, such as certain vegetables or fruits, can also produce a pink color with phenolphthalein and hydrogen peroxide.