The forensic luminol test for blood: unwanted interference and the effect on subsequent analysis

When no bloodstains are found by visual inspection in crime scene investigations the chemiluminescence (CL) produced in the luminol test for blood is a useful aid. The complex reactions that give rice to the bluegreen CL are facilitated by the catalytical activity of the hemoglobin in blood. The luminol test has a high sensitivity compared to other forensic blood tests. However it has a limited selectivity for blood. Different factors influence the potential to detect blood. Several compounds and substrates can trigger CL that can be mistaken for that of blood. One example is the sodium hypochlorite of bleaches. This is unfortunate because bleaches are sometimes used to clean areas at a crime scene. If a crime scene is allowed to air for one or two days this interfering effect diminish. Often are subsequent analyses of the blood visualized by the luminol test of interest. The test does not seem to affect subsequent use of presumptive blood tests like the phenolphthalein test. The test does not appear to have a severe inhibitory effect on neither PCR nor fluorescence based STR analysis. However prolonged exposure to the preparations used implicates a risk of DNA degradation. It should though be kept in mind that the often small amounts of blood visualized would not have been found at all by other reasonable means.