Blood volume testing
Blood volume testing is a forensic technique used to assess the quantity of blood shed at crime and accident scenes. This method is significant for forensic examiners as it provides insights into the nature of wounds inflicted on victims, helping to infer details about the incidents. The human body typically contains about 5 liters of blood, though this can vary based on individual factors like body size and fat content. By analyzing the volume of blood and the spatter patterns found at a scene, investigators can draw conclusions about the type, severity, and depth of injuries sustained by victims.
Additionally, blood volume testing can indicate whether a victim has been relocated post-injury by comparing the blood present at the scene to the expected blood loss from the victim. Collection methods for blood at crime scenes include using sterile containers for fresh samples and various techniques for dried blood, such as swabs or tape. In laboratory settings, forensic scientists calculate the blood volume based on the number of red blood cells or plasma present in the collected samples. Understanding the blood volume can also help estimate the nature of the wounds and the time elapsed since the blood was shed. Overall, blood volume testing is a critical tool in forensic investigations, aiding in the reconstruction of events surrounding violent incidents.
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Blood volume testing
Definition: Technique used to determine how much blood has been shed at crime scenes and accident scenes.
Significance: Forensic examiners can learn much about the wounds inflicted on victims of crimes from the volume of blood found at crime scenes. Blood volume testing may also be used to determine whether wounds were inflicted on victims at locations other than where the victims were ultimately found.
When blood is present at a crime or accident scene, a forensic team attempts to collect the blood or at least to determine how much blood was spilled at the scene. The human body generally contains about 5 liters (a little more than 5 quarts) of blood, but this amount is affected by factors such as body size and amount of fat tissue. The volume of blood present at a crime scene—and, sometimes, the blood spatter pattern—can inform investigators as to the types, depths, and seriousness of the wounds that caused the blood loss. Blood volume testing may also help to determine whether a victim has been moved—that is, if the amount of blood found at the scene is not consistent with the victim’s loss of blood, it is likely the victim was moved after the wounds were inflicted.
Any blood present at a crime scene is collected (or collection is at least attempted) and sent to a forensic laboratory for typing and identification. Fresh blood is collected in plastic containers. Dried blood may be collected in various ways: Fabrics with dried bloodstains may be transported to the lab, and sticky tape, such as fingerprint tape, may be used to peel spots of dried blood away from hard surfaces. Dried blood may also be collected with swabs or pieces of sterile cloth that have been moistened with distilled water or saline solution.
At the laboratory, a forensic scientist can estimate the blood volume found at the crime scene by determining how many red blood cells are present in the collected blood and then calculating how much whole blood would contain that many red blood cells. Alternatively, the scientist can determine how much plasma was left behind and calculate a blood volume from that figure.
When no body or victim is found at a crime scene where blood is present, knowing the volume of blood shed at the scene can help investigators determine what kind of wound was inflicted; for example, a minor cut produces only a small volume of blood, whereas a deep stab wound or an arterial puncture is likely to produce copious amounts of blood. A blood volume test can also help determine how much time was necessary for the amount of blood present to be left behind.
Bibliography
Geberth, Vernon J. Practical Homicide Investigation: Tactics, Procedures, and Forensic Techniques. 4th ed. Boca Raton, Fla.: CRC Press, 2006.
Genge, N. E. The Forensic Casebook: The Science of Crime Scene Investigation. New York: Ballantine, 2002.
Platt, Richard. Crime Scene: The Ultimate Guide to Forensic Science. New York: Dorling Kindersley, 2003.