Forensic serology.pdf
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Forensic serology Tarfa Altorki forensic biology 2024 Learning Outcome List the important definitions related to the topic Define different bodily fluids and their content Explain the different presumptive and confirmatory tests related to each bodily f...
Forensic serology Tarfa Altorki forensic biology 2024 Learning Outcome List the important definitions related to the topic Define different bodily fluids and their content Explain the different presumptive and confirmatory tests related to each bodily fluid type Forensic Serology Forensic serology is a branch of forensic science focused on identifying and analyzing biological evidence, including samples like blood, semen, saliva, sweat, breast milk, and other bodily fluids. The field generally is comprised of the detection of enzymes and antigens, as in the identification of seminal stains or blood typing (ABO and secretor status). Forensics Serology The serology section of a forensic laboratory deal with any or all of the following: characterization of unknown stains Identification of suspected body fluids Identify blood typing Analysing blood spatter for crime reconstruction Paternity testing Semen identification in sexual assault cases What is Blood? Blood is a specialized fluid in the body, made up of four key components: plasma, red blood cells, white blood cells, and platelets. It plays several vital roles, such as: u Delivering oxygen and nutrients to the lungs and tissues. u Carrying waste products to the kidneys and liver for filtration and detoxification u Transporting cells and antibodies to fight infections. u Helping regulate body temperature What is Blood? Blood is a mixture of many components: Cells inorganic substances (salts), enzymes water and proteins 55 % of blood content is plasma – mostly water and substances dissolved in it Most of the solid materials (by weight) are cells red blood cells, RBCs (erythrocytes) white blood cells (leukocytes) The average human body has about 5 litres of blood (less for females, more for males). Blood accounts for 8% of your weight Oxygenated blood is bright red , while deoxygenated blood is darker red due to the nature of haemoglobin RBC Erythrocytes (red blood contain haemoglobin and distribute Oxygen) Account for ~93% of all blood cells ~5 trillion cells/L Represent ~25% of all cells in the body Over 2 million made every second Live for about 120 days before recycled Haematocrit is a measure of RBC volume (45% of whole blood) h"ps://stock.adobe.com/ca/images/normal-‐red-‐blood-‐cells-‐ under-‐the-‐microscope/126269655 WBC Leukocytes (white blood Function in the immune system) Five types categorized by immune target and function Account for ~0.1% of all blood cells ~7 billion cells/L Live for 3-4 days before recycled Main component of pus Neural Compu@ng and Applica@ons volume 34, pages16089–16101 (2022)Cite this ar@cle Thrombocytes Thrombocytes ( responsible for blood clotting) Produced by fragmentation of larger stem cells Account for ~7% of all blood cells ~250 billion cells/L “Live” for 5-9 days before recycled Form long fibres to trap RBCs and form scab h"ps://fineartamerica.com/featured/1-‐ac@vated-‐platelets-‐ dennis-‐kunkel-‐microscopyscience-‐photo-‐library.html Plasma Plasma is the fluid portion of blood and accounts for 55% of the blood content. It is mostly water, and it contains the clotting factors, other proteins, hormones, and various chemicals. Serum is the liquid that separates from the blood when a clot is formed (serum = plasma clotting factors) h"ps://www.javatpoint.com/blood-‐plasma Components or tools? Three questions related to blood in the crime scene Three questions that must be answered by the forensic investigator: 1) Is it blood? 2) If yes, is it human blood? 3) If yes, can it be associated with an individual? Is it blood? Presumptive tests: Presumptive tests rely on haemoglobin's ability to catalyse the oxidation of certain reagents, usually resulting in a colour change. Oxidizing agent is usually hydrogen peroxide (H2O2). Is it blood? Presumptive tests Visible Stains(Phenolphthalein) Kastle Meyer: solution of phenolphthalein is applied to suspected blood stain, followed by hydrogen peroxide. A bright pink colour indicates the presence of blood. LeuchoMalachite Green: same procedure as K-M; produces blue-green colour in the presence of blood. Kastle Meyer LeuchoMalachite Green 1. Is it blood? Invisible Stains Luminol used for large areas where blood is suspected but not visible. If blood is present, it will glow. Must be viewed in darkness and photographed quickly. Luminol Presumptive test-‐‑ short comings Blood is not the only material that will cause presumptive test reagents to change colour. Horse radish & potatoes can also give positive results (these are unlikely to be at a crime scene, though). Luminol can give false positive results when exposed to household bleach, some metals, and some vegetables. Blood is the only body fluid that will give a positive reaction. Once we have a Positive results (blood is found) must be confirmed with Precipitin Test. 2. is it Human? Once a presumptive test indicates that a stain may be blood, the serologist must confirm that it is human blood. Precipitin test identifies the presence of proteins that are found only in human blood. Human vs non-‐‑Human Precipitin Test Procedure 1. Animal (usually a rat or rabbit) is injected with human blood 2. Animal’s blood forms antibodies 3. Antibodies are harvested from animal’s blood serum (“antiserum”) 4. In a test tube, an extract from the suspected bloodstain is added to the antiserum 5. If a precipitate forms where the two meet, it is human blood 3. Who’s blood is it? ABO DNA Easy process Hard process Fast Takes @me Less effec@ve in determining exact Accurate and effec@ve in determining suspects exact suspects ABO typing – why its not specific? Blood typing involves A blood type (40-‐42%) is most common determination of the antigens among Caucasians and those of present on an individual’s RBCs. European descent. type A blood – contain “A” B blood type (10-‐12%) is most common antigen on RBCs among African Americans and Thai type B blood – contain “B” antigen on RBCs Asians. type AB blood – contains both A AB blood type (3-‐5%) is most common and B antigens among Japanese & Chinese type O blood – contain no A or B popula@ons. antigens O blood type (43-‐45%) is most common Rh+ blood – contain Rh antigen among indigenous peoples and La@n Rh- blood – no Rh antigen Americans. So what have we answered? As a forensic serologist you have now determined: -‐ The fluid investigated is Blood -‐ It is human blood -‐ whom it may belong to What about other fluids? Seminal fluid Many of the cases sent to a forensic laboratory involve sexual offenses, making it necessary to examine exhibits for the presence of seminal stains. Confirmatory tests include microscopic examination, which are hard to come to due to the time limiting nature The best way to locate and at the same time characterize a seminal stain is to perform the acid phosphatase (an enzyme secreted into seminal fluid) colour test. A purple colour indicates acid phosphatase enzyme. Seminal fluid h"ps://www.researchgate.net/publica@on/ 335310521_Study_on_Acid_Phosphatase_enzyme_ac@vity_in_ semen_mixed_with_various_body_fluids Seminal fluid Another Presumptive is the p30 test for the presence of human prostate-specific p30 protein found in seminal fluid Seminal fluid UV light ‘woods lamp’ at 365nm h"ps://sperm-‐tracker.com/en/4-‐stk-‐lab Saliva Digestive fluid produced by parotid, sublingual, and submandibular glands inside mouth 99.5% water Mucus Enzymes (α-amylase, lingual lipase) Electrolytes: (Na, K, Ca, Mg, Cl, bicarbonate, PO4-3) Antibacterial compounds (thiocyanate, H2O2, and secretory immunoglobulin A) Saliva 4 presumptive tests for saliva: amylase (sensitive) phosphatase (sensitive, not specific to saliva) nitrite (sensitive to recent specimens) thiocyanate (sensitive, absence does not exclude saliva presence) Summary Forensic serology investigates the presence and authenticity of the fluids collected at the site of the crime(Saliva, semen or blood) Tests are divided between presumptive and confirmatory Tests are either Ab/Ag based OR chemical based. References Rana, M., Shrivastava, P., Srivastava, A., Kushwaha, P., Kumawat, R.K. (2023). Forensic Serology. In: Shrivastava, P., Lorente, J.A., Srivastava, A., Badiye, A., Kapoor, N. (eds) Textbook of Forensic Science. Springer, Singapore. Butler JM (2007) Short tandem repeat typing technologies used in human identity testing. BioTechniques 43:Sii–SSv Castro DM, Coyle HM (2013) Biological evidence collection and forensic blood identification. Forensic Sci Dep Henry C Lee Coll Crim Justice Forensic Sci Univ New Haven, p 300 Damelio R, Gardner RM (2001) Bloodstain pattern analysis: with an introduction to crime scene reconstruction. CRC Press, Boca Raton, FL Griffin TJ (2006) Principles of bloodstain pattern analysis: theory and practice. J Forens Identif 56:435 Identification of Saliva”. Nelson, David. Journal of Forensic Medicine, Volume 10, No: 1: January-March (1963). Pages 14-21. Questions
