The analysis of the properties and effects of serums (blood, semen, saliva, sweat, or faecal matter) is called Forensic Serology. According to Henry C. Lee, a forensics expert who has assisted law enforcement in over 6,000 major criminal investigations including that of O. J. Simpson—blood evidence is found most often in “crimes of violence such as homicide, assault, and sexual assault.” It may be in the form of fresh liquid, coagulated, dried, or as a small drop or stain, and each form involves a different method of preservation and collection. Determination of the type and characteristics of blood, blood testing, bloodstain examination, and preparation of testimony or presentations at trial are the main job functions of a forensic serologist, who also analyzes semen, saliva, other body fluids and may or may not be involved with DNA typing. Serology testing (assay) is largely used by forensic laboratories to analyze blood samples from suspects and bloodstains collected at the crime scene, in order to identify blood types of victims and assailants. The main objective of forensic tests, whether serological or other types, is to individualize samples through the identification of their sources.
Blood is the most common physical evidence in accidents, murder cases, and violent crime investigations. Besides blood, crime scene technicians may also find other stains and residues similar to blood in appearance at the scene, such as tomato sauce, red paint, or animal blood. To identify human blood, forensic scientists test samples at the crime scene with the chemical phenolphthalein, in an assay known as the Kastle-Meyer color test. Phenolphthalein releases hydrogen peroxide that reacts with an enzyme known as catalase in the blood. Catalase breaks down the hydrogen peroxide into water and oxygen, therefore releasing bubbles.
To identify human blood, forensic scientists test samples at the crime scene with the chemical phenolphthalein, in an assay known as the Kastle-Meyer color test. Phenolphthalein releases hydrogen peroxide that reacts with an enzyme known as catalase in the blood. Catalase breaks down the hydrogen peroxide into water and oxygen, therefore releasing bubbles. When red and white blood cells are removed from blood, the resulting clear golden yellowish liquid is serum. Serology is therefore the study of the properties of serum.
A particular laboratory may not have a serologist on staff, their functions being performed by a criminalist, a biochemist, a forensic biologist, or other technician. In certain specialized areas involving bloodstain examination (such as blood spatter analysis), courts will ordinarily qualify someone as an expert who has no formal education but specialized training and has conducted a sufficient number of examinations and accumulated enough reference patterns to be able to demonstrate the basis of their opinion. These kinds of experts are usually law enforcement personnel,and their testimony is most valid. Further, blood and bloodstain evidence is such an integral part of most crime scenes that a police investigator/bloodstain specialist might be found, in some jurisdictions, testifying on the ultimate issue.