Comparison of the sensitivity of presumptive blood tests Kastle-Meyer, O-Tolidine and Luminol on six fabric substrates
de Melo, Nicole
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Body fluid identification is important in the field of forensic science as it can provide valuable information to an investigation. An accurate method for detecting blood at a crime scene or on evidence is beneficial to an analyst or investigator. A piece of evidence may be any house-hold object or material; therefore, a test must be able to accurately detect blood on a variety of substrates. The most common preliminary testing method for blood is based on the peroxidase-like activity of hemoglobin. Tests such as phenolphthalein (Kastle-Meyer), Ortho-Tolidine (O-Tol), and Luminol utilize this method. The sensitivity of presumptive blood tests was evaluated using a series of diluted bloodstains on six fabrics: fleece, felt, linen, denim, flannel, and terrycloth. In addition to a direct testing method, two indirect methods were tested utilizing a piece of dry filter paper or a moistened cotton swab. The last portion of this study compared commercial field kits to the laboratory-prepared reagents. This study yielded overall sensitivities for Kastle-Meyer, O-Tol, and Luminol of 1:1000, 1:5000, and 1:10000, respectively. The direct testing resulted in a slightly lower sensitivity with fleece versus the other fabrics. Fleece also resulted in slower and weaker reactions compared to thinner fabrics such as denim, linen, and terrycloth. This suggests that highly absorbent fabrics, such as fleece, can have a negative effect on the sensitivity of catalytic color tests such as Kastle-Meyer and O-Tol. The indirect testing methods utilizing a moistened swab or a dry filter paper were less sensitive compared to direct testing methods. The field kits tested in this study mimic the methods of a moistened swab technique, and the results demonstrated that the field kits were about the same sensitivity or less sensitive compared to the indirect testing methods.