Latent blood traces detection

The investigation about bloody facts may lead to the suspicion of a place, whether it is a home or an outside such as the site of commission of the facts while it shows no bloodstains. Cleaning or natural erosion of these bloody traces is then considered.

Different chemicals exist to find (= detect) those bloody traces that are no longer visible (= latent). One of the most used and I participated in its development is the Bluestar®. It is a mixture whose active substance is Luminol or 5-amino-2,3-dihydrophthalazine-1,4-dione or 3- aminophthalhydrazideC8H7N3O2. This liquid solution emits light when it is in the presence of the ferrous ion, Fe2+, contained in hemoglobin (main compound of the blood). Due to its low quantum efficiency, it is necessary to be in the dark to observe this chemiluminescence.

This ferrous Fe2+ ion is also found in the hemoglobin of most vertebrates. Other so-called transition metals (Cu2+, Br+ …) as well as bleach can also catalyze this reaction. The reactions to these other substances are grouped in the false positives (obtaining a reaction that does not correspond to the desired substance).

However, the kinetics of the reaction to the blood: immediate and maximum reaction, 20-30s stage then decay of the reaction until its disappearance after 1min-1min30 eliminates many false positives.

This is why, after spraying, if a reaction is observed corresponding to that described above, a sample is taken to confirm the blood origin of the sample and to determine the genetic profile.

Although this product is not aggressive for DNA or the techniques used to determine the profile, it is not always possible to obtain a genetic profile because the chemical used:

  • has a higher sensitivity than the techniques used to determine a genetic profile,
  • reacts on the hemoglobin contained in the red blood cells (anucleate cells) while the DNA is found in the white blood cells (nucleated cells) knowing that the former are 600 to 1000 times more numerous than the seconds,
  • reacts on ferrous ion that is not degradable while cells are.

Philippe Esperança
Forensic Expert of the French Supreme Court

Bloodstain Pattern Analysis Expert of the Internation Criminal Court
IAI BPA Certification
Founder of the BPA sub WG of the European Network of Forensic Sciences Institutes (ENFSI)
International Association of Bloodstain pattern Analysts (IABPA) Vice President