Forensic Serology is defined by Bowman, Labbe and Mullings as “the science that deals with the identification, isolation, characterization of blood and bodily fluids from the victim, suspect, and the environment of the crime scene for the purpose of comparison to the known standards” (quoted, Olshaker, Smock, Jackson, p.235). It is commonly referred to as the “science of blood testing” (Phillips & Friedlander, p.19). However, forensic serology deals with not only blood but also other body fluids like saliva, semen, urine etc.
Forensic Serology is considered to be a very important area in forensic science. This is because traces of fluids or stains are frequently obtained at crime scenes primarily those involving homicides, rapes and assaults (Alley, p.46). The primary task of forensic serology is to analyze these fluids, also known as the physiological fluids, for genetic markers such as ABO antigens, enzymes and serum proteins (National Research Council, p. 157).
Serology and Forensic Serology
The field of Serology essentially deals with the analysis of body fluids. In the medical setting, these fluids are analyzed to assess the state of someone’s health. While in the forensic setting, the fluids are analyzed for determining their source at a crime scene. Another difference between these two setting i.e. medical and forensic is the samples themselves. In the former case, a clinical serologist deals with fresh and liquid samples of the fluids, which are usually taken recently from a person. In the later case, a forensic serologist deals with samples that are in stain form and in many cases these samples are degraded and deteriorated making the analysis process difficult (Eckert, p.46).
The job of a Forensic Serologist involving the physical evidence of a biological nature, according to Daniel D Garner, who is himself a forensic serologist, and includes immunohemotology, biochemistry, enzymology and human genetics (quoted, Kaye, p.349). The primary aim of Forensic Serology is the analysis, identification and most importantly individualization of body fluids and tissues, secretion, and excretions. The samples that are most frequently encountered are blood, semen and saliva. However, at times samples of perspiration, urine, gastric contents and feces are also occasionally examined for the purpose of characterization (Eckert, p.46).
The procedure of Forensic Serology usually involves submitting the samples in the form of dried stains from the crime scene to the laboratory for analysis. These stains may be retrieved from clothing or other materials from the scene, victim or suspect. In addition, standard known samples of the victim and / or suspect are also necessary for comparison and identification purposes. Control samples consisting of clean areas from which the stains were obtained is also necessary for the purpose of analysis (Eckert, p.46).
While there have been tests to identify blood ever since 1875, the technique only limited to identify whether a given stain was blood or not, and could not be applied to identify dry stains (Fisher & Nickel, p. 192). The technique for categorizing blood from different individuals into distinguishable groups was found by Karl Landsteiner in 1901 (Wecht & Rago, p.409). This technique was later known as the popular ABO system was the earliest identification technique available to people in the medico-legal professions (Fisher & Nickell, p. 193). In 1915, Leone Lattis created a method for determining the classification of blood from a dried blood stain, which had important implications for the criminologists. In the early 1960s, Forensic scientists turned to serum and cellular protein markers in their bid to expand their ability to differentiate between different individuals. Since the Lansteiner’s discovery of ABO system, there has been a lot of improvement in the scientific knowledge in the field of forensic serology. Throughout the 1970s and 1980s many advantages were made in the forensic application of mjnany serological blood typing markers, serum proteins, and red blood cells enzyme polymorphisms. As a result of all these scientific studies, there are more than 160 recognized antigens, 150 serum proteins and 250cellular enzymes (James & Nordby, p. 238).
However, the conventional methods of using the antigenic and protein markers were unstable and exhibited less specificity. Hence, the modern forensic serologists do not provide genetic marker comparisons for relating a fluid or blood stain to an individual. They do so by performing DNA analysis (Wecht & Rago, p.410).
Basic Forensic Serology Process
According to Alley (p.46), a forensic serologist, at the time of examining a suspected stain must answer the following three questions:
· Is it blood?
· If it is blood, is it hums?
· Is this is human blood, how closely can it be associated to a particular individual?
Conventional Forensic Serology follows an analytical approach for answering the questions above and has two main steps. The first step that must be taken while performing the forensic analysis is the identification of fluid making up the stain that is being analyzed. The next process of identification of the type of body fluid, which would link the stain to an individual using scientific methods such as ABO typing, polymorphic protein analysis, and / or DNA typing (James p. 48).
Generally in case of blood testing the following steps are followed: Visual Examination, Presumptive Testing, Confirmation Testing, Species Identification, and individualization testing. The first step i.e. visual examination is fairly easy in case the blood stains are very wet or fresh. However, in practical situations these stains are diluted, aged or degraded to such an extent that they cannot be characterized or predicted. Among all the steps given above only Visual Examination and Presumptive Testing can be done by scientists outside of a lab setting. By combining these two steps a forensic serologist has a better chance of collecting stains which can be later confirmed as being blood stains (James p. 48).
Presumptive Test – This is the essential starting point for the Forensic Serologic analysis, where a chemical test is done to indicate the possible presence of blood. Common presumptive tests for blood are phenolphthalein which produces a bright pink color in presence of blood, leucomalchite green which produces a blue-green color in presence of blood, and Luminol which highlights the blood stained surfaces in darkness for a bluish-white chemical luminescence. After the presence of blood is confirmed, tests are carried out to differentiate between human and animal origin by use of specific antibodies (Eckert, p.48).
Problems with Samples -As explained earlier, forensic serology as opposed to medical serology deals with samples that are degraded which makes the analysis of such stains very difficult. The degree of deterioration may depend on many factors which are not in the control of the forensic analyst. Hence, sample quantity and manner usually dictate the type of strategy used by the legal examiner to deal with a particular piece of evidence. Indeed sometimes the analysis of the stain may be not possible at all (James & Nordby, p. 237).
Limitations of Conventional Forensic Serology
The major drawback with this technique is the degree of specificity provided. A usual battery of such tests may just be able to characterize a person as a member of a larger population group who share the same markers. Depending on the markers, the likelihood that a randomly selected person may share the same markers with the person in question can range from 1 in 2, in case of type O blood, to 1 in several thousand, when many systems are typed and a relatively rare type is found (National Research Council, p. 157). This means that conventional serological techniques can have the possibility of excluding a person to including a whole lot of people who share the same type of markers, making the criminal proceeding difficult. Conventional serology is further limited by the fact that mixed fluid stains in which two or more contributors are involved may mask an individual donor. Also, it is found that only 70-80% of the population is secretors i.e. to say exhibit the ABO pattern in other fluids apart from blood, which further increases the risk of ambiguous identification (National Research Council, p. 158).
A combination of the above mentioned factor limits the power of conventional Forensic Serology as an individual identifier. Finally the results of such analysis are subjective which can be interpreted differently giving rise to different conclusion by equally qualified scientists.
Forensic Serology was the primary method for the analysis of body fluids found at the crime scene throughout the world from 1950s until late 1980s. At this time the analysis of body fluids for deoxyribonucleic acid DNA, started gaining hold and has now almost completely replaced the conventional methods for Forensic Serology.
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