Forensic Serology Identification Using Blood Groups Forensic Serology

Forensic Serology Identification Using Blood Groups

Forensic Serology – term used to describe a broad range of laboratory tests using reactions of blood serum and body fluid The serology section of a forensic laboratory may deal with any or all of the following: • blood typing • characterization of unknown blood • stain patterns for crime reconstruction • paternity testing • semen identification in rape cases • DNA techniques used for identification

The Composition of Blood is a mixture of many components: cells inorganic substances (salts) enzymes water 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)

How blood evidence is collected Most items Collected in clean, unused paper containers such as packets, envelopes, and bags. Blood pool – collect with gauze pad or clear cotton. Let air dry and refrigerate of freeze within 48 hours. Dried blood – wrap object in clean paper and place in paper bag. Small object: send whole object in. Large object: cover with paper and tape down or scrape it off with a knife.

Preserving Moist or wet biological evidence - Blood, body fluids, plants, etc. -1) Placed in clean, unused plastic containers at the scene and transported back to an evidence receiving area - Only if the storage time in sealed plastic is less than two hours - To prevent contamination of other evidence -2) Must be removed and allowed to completely air dry -3) Repackaged in a new, clean, unused, dry paper container -Reason for no more than 2 hours -Moisture allows the growth of microorganisms that can destroy or alter evidence

Forensic Characterization of Bloodstains Three questions that must be answered by the forensic investigator: 1) Is it blood? Benzidine Test Kastle-Meyer Test Hemastix (o-tolidine, TMB) Luminol Test 2) Is it human blood? Precipitin Test 3) Can it be associated with an individual?

Benzidine and Kastle-Meyer Color Test Preliminary Color Tests Benzidine Color Test - Benzidine is carcinogen so not used as often Benzidine + Blood Stain + Hydrogen peroxide = pink color Kastle-Meyer Color Test - phenolphthalein - Phenolphthalein + Bloodstain + Hydrogen peroxide = pink color

Human or Animal origin? Precipitin Test • Combine human antiserum and human bloodstain there should be agglutination • Requires only small amount of blood • Dried bloodstains as old as 10 - 15 years work Procedure: 1) Rabbits injected with human blood make antibodies in their serum 2) They are bled and the serum recovered 3) The serum is called human antiserum, because it will react to human antigens 4) It will cause coagulation when mixed with human blood

Precipitin Test

Luminol Test -Reacts with blood to produce luminescence - • Sensitive to blood that have been diluted up to 10, 000 times - • Destroys many important blood factors -Iron present in any blood in the area catalyzes the chemical reaction that leads to the luminescence revealing the

Luminol • Red blood cells contain hemoglobin (Hb) – the protein responsible for transporting oxygen • Each Hb contains four iron (Fe) containing hemes Heme structure

Hemastix© tests -strips to detect blood in urine. -But these strips can be used at a crime scene to detect fresh or dried blood -It detects the peroxide-like activity of hemoglobin.

Blood Antigens On the surface of red blood cells are chemical structures (proteins) called antigens The presence of antigens allow a living system to recognize foreign biological substances Antigens also impart specific characteristics to the red blood cells. These characteristics can be partly used to identify individuals Human red blood cells have more than 15 different antigen types that have been discovered

Blood Typing Blood typing involves determination of the antigens present on an individual’s RBCs The two most common blood typing systems used are the A-B-O method and the Rh method type A blood – contain “A” antigen on RBCs type B blood – contain “B” antigen on RBCs type AB blood – contains both A and B antigens type O blood – contain no A or B antigens Rh+ blood – contain Rh antigen Rh- blood – no Rh antigen

Blood Typing Blood also contains antibodies – proteins that recognize and bind to certain, specific antigens Blood Type Antigens on RBC Antibodies A A anti-B B B anti-A AB AB none O none both A & B

Blood Typing When blood containing a specific antigen is mixed with blood containing the corresponding antibodies, the blood clots The clots can then be removed by the host system

Blood Typing Human serum containing specific antibodies can be purchased Separately mix a drop of unknown blood sample with drop of each anti-serum Reaction between blood anti-serum No reaction between blood anti-serum

Blood Typing Example A sample of unknown blood is mixed with three antisera samples: Tube 1 (Anti-A): No reaction Tube 2 (Anti B): No reaction Tube 3 (Anti Rh): Cloudy reaction In terms of the A-B-O and Rh systems, what type blood is the sample? The ABO antigens are not confined to RBC; 80% of Americans are secretors, found on other cells

Blood Typing Example A sample of unknown blood is mixed with three antisera samples: Tube 1 (Anti-A): No reaction Tube 2 (Anti B): No reaction Tube 3 (Anti Rh): Cloudy reaction In terms of the A-B-O and Rh systems, what type blood is the sample? O positive The ABO antigens are not confined to RBC; 80% of Americans are secretors, same antigens found on other cells

Blood Splatter Analysis Categories of Bloodstains: Passive (dripping) Transfer (smearing) Projected Bloodstains occur in shootings, trauma from blunt weapons, hacking, or slashing attacks.

Projected Bloodstain Analysis Two Important Determinations: a. direction of splatter b. angle of impact with surface sin = (width drop / length drop)

Spines, Satellites, Elongation Tails Splines Satellites Elongation Tails Satellites

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