A non-destructive method for distinguishing human blood from the blood of 11 animal species is described in a paper published in Communications Chemistry. This technique could be developed to rapidly confirm or deny the human origins of bloodstains found at crime scenes.
Bloodstains provide one of the main sources of DNA evidence, but current blood tests typically destroy the sample and any DNA evidence along with it. They can also provide false-positive results that indicate human origins where there are none. The ability to confidently and non-destructively discriminate between human and animal blood is therefore highly desirable for forensic purposes, particularly for hit-and-run cases, where a suspect might claim that an incident involved an animal and not a human.
Igor Lednev and Ewelina Mistek-Morabito combined a technique called attenuated total reflection Fourier transform-infrared (ATR FT-IR) spectroscopy with statistical analysis to differentiate between human and animal blood. The authors built statistical models using human, cat, dog, rabbit, horse, cow, pig, opossum and raccoon blood samples, and validated the models using deer, elk and ferret blood samples. They selected animal species that are common house pets, consumed by people, or can be involved in wildlife crimes or hit-and-run accidents. Validation of the model with blood samples from species used in the training data set led to one misclassification out of 290, while validation using deer, elk and ferret blood samples led to no misclassifications.
Since some ATR FT-IR spectrometers are portable, this technique could be developed for, at-the-scene analysis.
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