serology. study of bodily fluids: blood, semen, saliva, urine, vaginal secretions, and excrement dna...

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