Blood testing is used in forensic science to help identify individuals who may be involved in a crime. Blood analysis is used in cases involving a blood-stained crime or accident scene, often to help identify possible victims. The blood itself can be tested for various elements, and can also be used to provide a DNA sample, which provides far more detailed data on the individual who was the source of the blood.
Blood testing in forensics is done by scientists whose job is to discover and examine physical traces of blood. This evidence is used to establish an association between criminal suspects, victims, and the scene of the crime. Forensic scientists will gather blood found at a crime scene and prepare it for a series of chemical and molecular tests. These tests provide data which is compared to a sample from a known individual. When data matches, is establishes a link between the individual and the crime that can be presented in a court of law.
Blood analysis begins with a process of verification of a sample found at a crime scene. In some cases it may be necessary to establish that the fluid is actually blood. Chemicals are applied to samples that change to a certain color for blood. For example, luminol spray can be used to detect tiny traces of splattered blood, and will even highlight blood which was previously scrubbed away.
One of the first steps in forensic blood testing is to determine blood type. This is typically done in a forensic investigation using the ABO system, which is a straightforward test that can quickly exclude an individual when the blood samples are not a type match.
Forensics blood tests also look at Rh factor, which is a known protein found in some people's blood. The Rh factor results in blood being positive (A+) or negative (A-), and is another step in categorizing blood to make more specific matches to individuals.
Deoxyribonucleic acid (DNA) contains the genetic blueprint of an individual, and samples can be taken from blood to get a much more accurate match with the sample of an individual. When a highly verifiable match of blood samples is required, forensic scientists will conduct a DNA test. Blood samples are often used, but other bodily fluids can also provide a DNA sample.
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