Forensic Serology: A Complete Overview

Forensic serology


Forensic serology is the examination of various physiological fluids, including blood, semen, saliva, urine, vomit, fecal matter, and perspiration (sweat), for judicial proceedings. The presumptive test is used to start the detection process since it suggests that a particular bodily fluid might be present, but the other confirmation test verifies its presence. The confirmatory test verifies what the fluid is made of.

In criminal investigations, this is done to aid in identification. As it associates the crime with the offender or excludes any innocent parties, it is significant in the criminal justice system.

Also Read: How to become Forensic Serologist?

Forensic serology is the use of immunological and biochemical techniques to detect the presence of body fluid or tissue samples found during a criminal investigation and to perhaps further characterize the sample’s genetic makeup to identify its most likely contributors (Ballantyne, 2000). Instead of using DNA genetic markers, polymorphic antigens and the proteins found on blood cells are used in this case for genetic characterization. Thus, forensic serology is the study and testing of bodily fluids like blood, semen, perspiration, urine, saliva, feces, and other fluids, mostly for identifying reasons in criminal/medical-legal investigations.

One of the most frequent and crucial types of evidence found during forensic investigations is blood. It is frequently found in incidents involving murder, assault, and terrorist attacks, including bombings. In the criminal justice system, blood evidence is important because it can either prove or disprove a person’s involvement in a crime. Bloodstain patterns can also aid in the reconstruction of a crime scene by providing details regarding the relative positioning and movements of the perpetrator and victim there.

It’s crucial to determine the kind, source, and other details of the blood and blood stains at the crime scene. In this context, preliminary examinations are being conducted to determine whether the retrieved fluid is blood and whether it has a human origin. Further investigation is carried out to identify other features after the human origin of the blood or blood stain has been established. Blood typing is first applied to the blood stain. Additionally examined are the person’s blood’s proteins, enzymes, and antigens. Additionally, white blood cell HLA typing from blood analysis may be done.

To ensure that a blood sample is from a human bodily fluid and not an environmental source, a thorough collection of the stain and a nearby area devoid of the stain is necessary. Since ABH antigens can be present in other mammals, bacteria, wood, dirt, dust, and other locations, careful collection is essential. Additionally, environmental microbes can enzymatically change blood group antigens. Coffee beans, as well as Clostridium spp., Bacillus spp., and Aspergillus niger, can alter or get rid of specific blood group components. When the test for H is negative, it is advised to test for A or B.

In addition to blood, it is also feasible to test for anti-A and anti-B in stains or fresh body fluids; however, it’s crucial to be careful of false negatives and positives.

MCQs On Forensic Serology

Currently, DNA technology has taken the place of blood sample testing which looked for particular proteins and enzymes. The DNA typing technique is widely recognized by all international courts of law. Blood evidence, either by itself or in combination with other trace evidence found at the crime scene, can be extremely helpful in resolving criminal cases.

It answers three questions:

A. what is the nature of the biological evidence sample? (Identification )

B. what is the species origin of the sample (whether human or animal origin)?

C. Whom the biological evidence belongs (individualization)?

After meticulously gathering the biological evidence from the crime scene, the examination is completed.

There are various categories of bodily fluids that are most frequently found at crime scenes.


Blood is a fluid that circulates continuously and carries essential elements like nutrients, oxygen, hormones, etc. It moves metabolic wastes like carbon dioxide and other byproducts out of the body.



•  a vehicle for all substances to travel in

•  Providing defense by displaying immunological reactions

•  Thermo-regulation

•  Coagulation by Clotting factor fibrin

•  Acts as a messenger by transporting hormones.


It consists of two major parts:

•  Cellular part: this comprises RBCs ( Red Blood Cells ), WBCs ( White Blood Cells ), platelets

•  Fluid parts: this comprises plasma.

The red color of the blood is due to the presence of a pigment called hemoglobin.


Blood provides important details regarding what occurred during the crime. Blood is useful in demonstrating a person’s connection to the murder scene. Blood can occasionally be used to understand the circumstances around death or how a crime was committed. Blood is typically discovered in violent crimes such as murder, rape, hit-and-run accidents, etc.


The fluid secreted by the male reproductive system is known as Semen. Seminal fluid is another name for it. Semen has a translucent appearance and a white, grey, or even yellowish hue. A human guy produces between 2 and 5 ml of total semen during each ejaculation.


Because it can fertilize the female ovum, it facilitates successful fertilization.


It is made up of seminal plasma and spermatozoa. The male generative cell is the spermatozoa, whereas the seminal plasma maintains the sperm cells’ viability.

The seminal fluid is produced by the secretions of four glands.

•    Testes,

•    Seminal Vesicle,

•    Prostate gland

•    Bulbourethral gland.


Since it helps to establish that sexual or physical contact took place in situations of sexual assault, it is regarded as the most significant piece of evidence. The perpetrator can be located by additional DNA analysis. It can be found in the victim’s vagina, on clothing, on bed linens, etc.


In humans, urine is a by-product of cellular metabolism. It is created by the kidney and travels via the ureters, the urine bladder, and the urethra before being expelled. Its hue ranges from clear to golden. An individual produces 1.4 liters of pee on average each day.



•    Body waste removal regulates the concentration of metabolites and electrolytes

•    controls blood’s pH homeostasis

•    controls blood pressure


Water, urea, chlorides, sodium, potassium, creatinine, uric acid, ammonia, phosphates,  and sulfates make up the majority of its composition.


Strangulation cases, violent cases, poisoning cases, sexual assault cases, etc. all involve it. It can be used to determine whether there are any toxins, proteins, or medications present. For DNA analysis, urine is not a great source of evidence.


Saliva (referred to as spit) is an extracellular fluid produced and secreted by salivary glands in the mouth. It is a complex fluid where the various constituents act alone to perform different functions in the oral cavity.


•    Acts as a lubricant

•    Digestion of food

•    Maintenance of oral hygiene

•    Improves taste

•    Maintains the pH of the mouth


•    99% of water

•    electrolytes such as sodium, potassium, calcium, magnesium, chloride, bicarbonate, etc.

•    enzymes such as α-amylase, lysozyme, etc


For criminal investigations, identifying saliva stains may be crucial. The use of drugs or alcohol, animal bites, sexual assault, and poisoning are all examples of it. Any food item, including cigarettes and handkerchiefs left at crime scenes, may contain them. The body of a victim of sexual assault could be covered in saliva stains. It may indicate the DNA’s origin or it may specify the blood type.


The fluid secreted by the exocrine sweat glands, also known as sudoriferous glands, is known as sweat.

Adults can perspire as much as 2-4 liters per hour or 10–14 liters per day.


•  Thermo-regulation

•  Regulates the levels of electrolytes


•    majorly water

•    trace amounts of lactic acid, and urea.

•    minerals such as sodium, potassium, calcium, magnesium, copper, iron


Sweat can be seen in cases of sexual assault, domestic violence, drug use, or abuse. At the scene of the crimes, a criminal frequently leaves behind clothing. These clothes might have stains from perspiration. Their posture will very clearly reveal where they came from. It may also provide information about a specific medicine or illness.


The solid or semisolid remnants of food that the small intestine was unable to digest is known as feces. The leftovers are further broken down by bacteria in the large intestine. It only contains a limited amount of metabolic waste products, such as bilirubin which has undergone bacterial modification and dead gut epithelial cells.

During defecation, feces are expelled through the anus or cloaca.


•    Excretes out as a waste product.


•    75% of water

•    25% of solid

•    30% of solid matter is indigestible food matter

•    10-20% is cholesterol


•           Fecal deposits on garments are frequently identified in situations of homosexuality or homosexual abuse. It might have been brought to the crime scene by the perpetrator’s odd mental aberration, anxiousness, or a natural desire. It can be seen in apparel, footwear, etc.


Traditional serological methods, like those mentioned above, can be used to test for various bodily fluids, although they have significant limitations. First off, not all body fluids have a trustworthy confirmatory test, and those that do usually need a bigger sample of the suspected stain to perform the test. If the forensic sample being analyzed is little, to begin with, this may be restrictive.

Additionally, serology is frequently performed before any downstream analysis like DNA, thus if the initial sample is small, completing serological tests and effectively collecting a DNA profile may not be possible. Micro RNAs are a newly emerging technology that may help scientists identify physiological fluids more successfully and with fewer samples.

Small, non-coding, single-stranded RNA molecules called micro RNAs (miRNA) control the translation of messenger RNA (mRNA) or mark it for degradation to control the expression of genes.

According to the notion, different miRNAs would be present in varying amounts in specific fluid or tissue types since each of those tissue types should have distinct proteins and mRNA based on their role in the body. This is because miRNAs have a regulatory role in the body. The fact that miRNAs are small in comparison to other cellular components makes them a better target for forensic examination than other tissue indicators. This is significant because casework samples aren’t always going to be in perfect condition. Finally, miRNAs have the potential to be extracted and examined concurrently with DNA for biological sample analysis, integrating the two procedures into one and saving both time and sample.

Several commercially available kits, such as the Solid Phase QIAmp DNA small kit, can be used to extract miRNA. As with the QIAmp kit, the extraction technique should ideally be able to extract DNA and miRNA simultaneously, cutting down on the number of processes and sample requirements. Similar to typical DNA samples, quantitative Real-Time PCR can be used to quantify miRNAs. However, this would need the development of primers and probes specific to the miRNA targets. Mirna amplification necessitates an additional step before the PCR procedure, unlike standard DNA profiling. To transform the miRNA fragments into their complementary DNA (cDNA) pieces, reverse transcription is necessary for miRNA. Once this conversion has taken place, the sample’s other DNA can be amplified using PCR, and the cDNA can then be isolated from it and observed using a capillary electrophoresis procedure. The miRNA targets would require the development of cDNA-specific primers. The resultant electropherogram includes the sample’s STR profile as well as a peak indicating which miRNA is present in that sample.

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