By: Don Penven
The purpose of BloodTips is to provide quick tutorials in the use of the most frequently used blood screening methods at crime scenes. These tests are PRESUMPTIVE in nature. They, like narcotic and drug field tests, serve a singular purpose—they provide the crime scene investigator with the knowledge that a particular stain possesses the possibility that it is blood, and these tests are not a substitute for crime laboratory analysis.
The most commonly employed field tests available for use at crime scenes are:
- Phenolphthalein
- Leuco malachite
- Luminol
A variety of commercially-available packaging methods permit simplified, uncomplicated use of these reagents at crime scenes. Each BloodTips post will present a simplified application procedure while existing posts on this blog provide more in-depth coverage of these techniques.
Uses are strongly advised the conduct their own experiments using each of these processes prior to any use at a crime scene. The crime scene investigator is also encouraged to examine the Material Safety Data Sheets (MSDS) readily available from the manufacturer to learn of any hazards that may exist when using these reagents:
To download these MSDSs, please use the following links:
Phenolphthalein: Download DCB100A Download DCB100B
Leuco Malachite: Download DCB200A Download DCB200B
Luminol: Download DCB300
The Contact Method of Testing
In order to preserve the integrity of the stain to be testing, we strongly recommend that the Contact method of stain sampling be used in all cases.
Procedure:
- Using a clean piece of filter paper, moisten it by adding a few drops of ethyl alcohol or distilled water, whichever is indicated on the instructions accompanying the particular reagent.
- Press the wet filter paper against the suspected stain for a few seconds.
- Please the filter paper test strip on a clean surface (paper towel, napkin, etc.)
- Add the test reagent to the stain.
In the case of phenolphthalein a pink stain will develop in a few seconds indicating the presumptive presence of blood.
In the case of leuco malachite an intense blue/green stain will develop in a few seconds indication the presumptive presence of blood.
In the case of luminol, the presumptive presence of blood will be indicated to a bluish-white luminescence. This luminescence is only visible in near total darkness.
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