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Forensic Serology The dead cannot cry out for justice; it is a duty of the living to do so for them. Ch 13 237-256 Lois McMaster Bujold, Diplomatic Immunity, 2002 Terminology Chemiluminescence – the emission of light from a chemical reaction Hemoglobin – the oxygen carrier that gives red blood cells their color Serum – a liquid that separates clotted blood Antibodies – proteins in the blood that tag, destroy, or neutralize bacteria, viruses, or harmful toxins, producing an immune response Antigens – foreign substances in the body capable of causing disease (the presence triggers an immune response Agglutination – a type of allergic reaction where red blood cells clump together in response to a a particular antibody Antiserum – human or animal serum containing antibodies that are specific for one or more antigens What is Serology? The study of bodily fluids is called serology. 1/12 is blood (cells suspended in liquid) urine, saliva, semen, sweat The fluid part of blood is plasma. Makes up 55% of the blood Composed of 90% water and 10% metabolites, waste, salts, ions and proteins Blood at the Scene of a Crime Blood is often found at the scenes of violent crimes. Its location, distribution and pattern can help reconstruct the scene Is class evidence until DNA individualizes it Human or Animal? Once investigators have determined that a stain is blood they will next test it to find out if it is human or animal. precipitin test – the standard method Uses animal serum that contains antibodies specific to human antigens; reacts to agglutinate human blood. What is blood made of? The solid portion of blood is made up of 3 principle types of cells: Red cells, which contain hemoglobin. White cells, which are primary cells of the immune system. (They produce antibodies) Platelets, which start the clotting process. When the solid clotting material is removed it leaves behind a pale yellowy, watery fluid called serum. Tests for Blood Visual observation followed by a positive chemical presumptive Catalytic color tests – employ the chemical oxidation of a chromogenic substance by an oxidizing agent catalyzed by the presence of blood Produce a visible color or light reaction Phenolphthalein (Kastle-Meyer) Tetramethylbenzidine (Hemastix) Chemiluminescence and fluorescence – involve spraying a mixture on to a suspected area and observing the result Luminol Flourescein Phenolphthalein - Produces a bright pink color when used in testing suspected blood. Tetramethylbenzidine Commonly used as Hemastix, the test consists of a plastic strip with a reagent treated filter paper tab at one end. Positive result when the color changed from yellow to green or green-blue. Luminol The forensic application involves spraying a mixture of Luminol over an area thought to contain traces of blood. Outlines and details are visible 30 seconds after spraying. Flourescein Similar to Luminol, however, it requires an alternate light source (ALS). Will not react if the are has been previously treated for bleach. ABO System 1901- Karl Landsteiner recognized that all human blood was not the same. Worked out the ABO classification system Discovered why so many patients died after a transfusion for no apparent reason Discovered the Rh factor in the blood On the surface of each red blood cell, millions of characteristic chemical structures called antigens can be found. Are responsible for the different blood types In the ABO system there are 2 types of antigens, A and B. Type A blood cells have A antigens Type B blood cells have B antigens Type AB blood cells have both A&B antigens Type O blood cells have neither antigen Rh Factor The Rh factor is important for classifying blood type. Sometimes referred to as the D antigen People who have it are called Rh positive (Rh+) People who don’t have it are called Rh negative (Rh-) 85% of people are Rh+ Process of Agglutination Several drops of each kind of antiserum are added to separate samples of blood. If agglutination (clumping) occurs in the suspension to which only the anti-A serum was added, the blood type is A. Clumps with anti-B, type B In both, AB None, O Red blood cell compatibility table Recipient [1] [1] Donor O- O+ A- A+ B- B+ AB- AB+ O- O- O+ O- O+ A- O- A+ O- O+ A- A+ B- O- B- B+ O- O+ B- B+ AB- O- AB+ O- O+ A- A+ B- B+ AB- AB+ A- A- B- AB- Distribution of blood types O A B AB 43-45% 40-42% 10-12% 3-5% O+ 39% O- 6% A+ 35% A- 5% B+ 8% B- 2% AB+ 4% AB- 1