serology. study of bodily fluids: blood, semen, saliva, urine, vaginal secretions, and excrement dna...
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Serology
Serology
Study of bodily fluids:
blood, semen, saliva, urine, vaginal secretions, and excrement
DNA can also be collected from these samples.
Blood
1. Plasma- fluid part of blood– 90% water– 10% salts, ions, proteins
2. Red blood cells
3. White blood cells
4. platelets
Karl Landsteiner
• 1901
• Determined blood types (ABO and Rh)
• Red blood cells have proteins (antigens) on the surface of the cell
• Blood type A – has A antigens on surface
• Blood type B- has B antigens on the surface
• Blood type AB- has A and B antigens
• Blood type O – neither A nor B antigens
Secretors
• Some people have blood type antigens in other body fluids besides their blood
• Collect info from location, distribution, & pattern of blood stains==> reconstruct events of the crime
• Blood typing --> class evidence
Class Evidence
• Can be associated with a general group
• Cannot be associated with an individual source
• Ex. Blood types
Individual evidence
• Can be traced back to an individual source.
• Ex. DNA sample from blood
Controls
Positive control - known blood will cause the color to appear (solutions are working)
Negative control - absence of blood- no appearance of color (shows there is no contamination)
More on presumptive tests
• In most presumptive tests, the solution that is used for the test changes color when it comes in contact with blood.
• The substances in the blood that cause the color change are
a) Hemoglobin
b) Peroxidase
Presumptive Tests for Blood
(screening tests)
A negative result means that the sample can be ruled out as being blood.
• A positive results means that the sample is very likely blood. – Need to be confirmed by more specific tests
Presumptive Tests for Blood
• Hematest tablets or Hemastix strips
• Kastle-Meyer solution
• Luminol
Hematest or Hemastix
• Tablets or strips will turn blue/green in the presence of blood
• This tablets or strips are available in some pharmacies
Kastle-Meyer color test
• Aka: phenolphthalein test
• Produces a bright pink color in the presence of blood.
• False positives can be given by potatoes or horseradish, or shrimp cocktail
Luminol
• Spray that makes blood residue glow a bluish color in total darkness.
• Chemiluminesce = glow
• Glow only lasts for a short time (second to minutes)
Is the blood human?
• Use the precipitin test
• To understand how this test works, you need to understand:
• Serum• Antigens• Antibodies• Agglutinate• Antiserum
Confirmatory tests for blood
• Takayama & Teichmann tests– When the right chemical solution is added to a
bloodstain, crystals will form if the stain really is blood.
– Crystals are visible under a microscope
• Precipitin test – shows if blood is human or animal
• Serum -A liquid that separates from whole blood
• Antibodies- proteins produced by the body’s immune system that target bacteria, viruses, poisons (anything foreign)
• Antigens- any foreign substance that causes an immune response in the body
• (production of antibodies)
• Agglutination- clumping of blood
• Anti-serum – serum from humans or other animals that contain antibodies to a specific antigen
How is anti-serum produced for blood tests?
• Ex. Human blood is injected into a rabbit.
• The human blood is foreign to the rabbit, so the rabbit produces antibodies against the human blood.
• Serum from the rabbit is collected. The serum contains antibodies to human blood.
• If the serum is applied to an unknown sample of blood, the antibodies in the serum will bind to the blood if the unknown is human blood.
• The binding of the antibody to the blood causes clumping of the blood cells
• The clumping (agglutination) is very visible.
• If the unknown sample is not human, there will not be any clumping.
• Why test blood when DNA is a more precise form of testing?
a)DNA testing slow
b)DNA testing much more expensive
History
• Karl Landsteiner- Austrian immunologist and pathologist
• 1901- showed blood types to be A, B, AB, and O
Type Possible
genotypes
Antigens present
% of US pop.
A AA
AO
A 40
B BB
BO
B 10
AB AB A and B 5
O OO none 45
Probability of having a blood type
• What is the chance of being B +?
• B 10% = 1/10
• Rh += 85% = 85/100
• 1/10 X 85/100 =85/1000
Packaging blood from a crime scene
• Blood must NOT be put into an airtight container
• Any moisture in the container will lead to mold and mildew forming.
Rh factor
• There is another protein (Rh) found on the surface of blood cells.
• Also known as D antigen
• 85% of the population is + for Rh.
• If you have this protein you are +.
• If you do not have this protein, you are -.
Questions to ask about fluids at a crime scene
• 1. Are the stains blood, semen, saliva, or something else?
• 2. Are the stains from a human or another animal?
• 3. Who or what is the source of the stain?4. How, why, and when did they get deposited on items at the scene?
Whose blood is it?
• Human blood has about 100 different antigens.
• Only test for a few.
• More than a dozen blood typing systems
• The most common is the ABO system.
Blood Spatter Evidence
• Angle of impact• Gushing pattern (arterial spurts)• Back spatter• Cast-off pattern• Contact stain• Direction of flight• Drawback effect• Drip pattern
• HVIS= high velocity impact spatter
• MVIS
• LVIS
• Misting-fine spray
• Parent drop – has satellite spatters
• Area of convergence
• Area of origin
• Spine
• Swipe pattern
• Void- area w/o blood stain