ABSTRACT
Blood evidence, for example, a dried bloodstain, is commonly associated with criminal investigations. Preliminary and confirmatory assays are performed to ensure that a sample is in fact blood. A positive reaction of a preliminary assay indicates that the presence of blood is a possibility, but the presumptive assays are not specific only for blood and therefore should not be considered to be conclusive. In contrast, a negative assay suggests that blood is absent. Preliminary assays are quick, sensitive, and easy to perform. Thus, they may be used for screening and preliminary examination of stains prior to utilization of other types of analysis such as forensic DNA testing. Additionally, these assays can be used as search methods to locate stains of possible blood origin at a crime scene. Additional confirmatory assays should be conducted later if necessary.
