6533b7d6fe1ef96bd1265bdf

RESEARCH PRODUCT

Investigation of bloodstains: false negative results of the benzidine test

subject

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Since the discovery of the Benzidine Test, this method has been considered absolutely reliable for the generic diagnosis of bloodstains. The authors reviewed support the existence of false positive results, as the subtract in the coloration reaction the peroxidases may be found in numerous natural products [ 11. There is also general agreement with the false negative results: a negative result provided by the Benzidine Test indicates that the stain is not blood [2]. Given the strong certainty offered by most works of forensic medicine and criminology, most countries Spain included use this technique as a screening method in the investigation of bloodstains: when the result is negative the investigation finishes with the conclusion that ‘the stain was not a bloodstain’. In our Criminology Laboratory, we have observed that there are substances which mixed with blood provide false negative results in the Benzidine Test. It is well-known that the Benzidine test or oxidase reaction is based on the existence of a blood oxidizing potential which becomes apparent through a change in the colour of the Adler Reactive (benzidine in saturation in acetic acid). Taking this into account, our working hypothesis considers that this potential could be counteracted by the existence of some substances with a high reduction power, which may be mixed with the sample investigated. Thus, despite the existence of blood in