Serology
Serology
Serology is the study of blood and other body fluids including sweat, semen, saliva, and urine.
A forensic serologist may analyze a variety of physical evidence with the intent of finding, identifying and individualizing stains of biological origin.
Blood Characteristics
Blood:
A complex mixture composed of cells (45%), enzymes, proteins, and plasma (55%).
It is composed of three main cells: erythrocytes,
leukocytes, & thrombocytes.
Erythrocytes (RBC):
The most abundant cells in our blood.
They are produced in the bone marrow.
They are responsible for oxygen distribution (contain hemoglobin).
Leukocytes (WBC):
Part of the immune system & destroys pathogens.
Thrombocytes (Platelets)
Responsible for blood clotting.
Plamsa:
Yellowish fluid portion of the blood.
Principally made of water.
Contains electrolytes, nutrients and vitamins, hormones, clotting factors, and proteins such as antibodies.
Blood volume makes up 8% of total body weight.
Average adult has five liters of blood.
A 40% (2L) loss of total volume results in irreversible shock (death).
A 1.5L loss of total volume results in disabling a person.
There are one billion RBC in 2-3 drops of blood.
For every 600 RBC, there are about 40 platelets and one WBC.
Blood Terminology
Antigens:
Responsible for blood type characteristics.
On the surface of RBC.
A protein that stimulates the immune system to produce antibodies.
More than 15 blood antigen systems have been identified.
Antibody:
A protein that reacts with an antigen.
Produced by WBC.
They recognize and bind to certain, specific antigens (agglutination).
Agglutination:
Clumping of RBC which occurs if blood types with different antigens are mixed.
ABO System
Karl Landsteiner (1901)
Discovered the ABO blood system of blood typing.
Leon Lattes (1915)
Discovered a way of typing dried blood using saline to determine the ABO system.
Blood type is inherited.
It can be used to include or exclude a person as a suspect.
It can not absolutely identify a suspect.
It can absolutely exclude a suspect.
The groups are based on having an A,B, both or no antigens on RBC.
There are four different blood types: A,B,AB, and O.
[pic]
[pic]
Distribution of blood types:
[pic]
ABO System
Rh Factor (+ or -)
Rh stands for rhesus factor, first identified in rhesus monkeys in 1940.
Rh is antigen D on the surface of RBC.
It is inherited separately from the A & B antigens.
Presence of antigen D, Rh positive.
Absence of antigen D, Rh negative.
85% of Caucasians, 94% of African Americans, and 99% of all Asians are Rh positive.
Blood Donation
AB is the universal recipient.
O is the universal donor.
If you are Rh +, you can accept + or – .
If you are Rh -, you can only accept -.
Analysis of Blood
Three questions must be answered by the forensic serologist:
1. Is it blood?
2. Is it human blood?
3. Can it be associated with
an individual?
Analysis of Blood
Is it Blood? (Presumptive Tests)
Kastle-Meyer Color Test:
-Phenolphthalein, hydrogen
peroxide, and suspected blood
stain are mixed; positive
reaction indicated by a deep
pink color.
-It reacts with iron in
hemoglobin to produce a pink
color.
Is it Blood? (Presumptive Tests)
Kastle-Meyer Color Test:
-Results are not definite.
-Substances other than blood
may produce the color
change (potatoes and
horseradish).
Is it Blood? (Presumptive Tests)
Hemastix Test:
-Used in the field by
investigators.
-A dipstick moistened with
distilled water is placed in
contact with the suspect
blood.
Is it Blood? (Presumptive Tests)
Hemastix Test:
- It reacts with iron in
hemoglobin causing a green
color change.
Is it Blood? (Presumptive Tests)
Luminol Test:
-A test for blood that
produces light
(luminescence) when it
reacts with blood.
Is it Blood? (Presumptive Tests)
Luminol Test:
-Extremely sensitive-it is
capable of detecting blood
stains that have been diluted
up to 300,000 times.
Is it Blood? (Presumptive Tests)
Luminol Test:
-Limitations:
1. Reacts with copper
containing alloys, certain
bleaches and citrus fruits.
2. Residual bleach will cause
the entire scene to glow.
Analysis of Blood
Is it Blood? (Presumptive Tests)
Luminol Test:
-Limitations:
3. Its presence prevents
other tests from being
performed. (DNA analysis
can still be performed).
Analysis of Blood
Is it Blood? (Presumptive Tests)
Leucomalachite Test:
-A mixture of acetic acid,
distilled water, leucomalachite
green, and sodium perborate
will turn a sample green in the
presence of blood.
Analysis of Blood
Is it Animal or Human?
Precipitin Test:
-Based on the theory of
antigen-antibody reactions.
-An animal (rabbit) is injected with
human blood.
-The animal creates antibodies that
can be recovered and used to test
for various human blood antigens.
Analysis of Blood
Is it Animal or Human?
Precipitin Test:
-The recovered antibodies
are called human
antiserum.
Precipitin Test:
-To test for human blood,
human antiserum and an
unknown blood are put
together—if the blood is
human a precipitate will form.
Analysis of Blood
Is it Animal or Human?
Differences:
-Platelets and leukocytes do
not differ significantly.
-Mature human RBC lack a
nucleus.
Analysis of Blood
Can it be Individualized?
DNA Analysis:
-Characterizes bloodstains to a
particular individual using blood
factors.
Blood Spatter Interpretation
It applies principles from biology, chemistry, physics, and math to interpret bloodstain patterns within a forensic setting.
It is used to determine what
happened at a crime scene &
the sequence of events that
took place.
It can determine:
-Location and description of
individual stains and
patterns
-Mechanism that created
the stains
-Direction blood droplet was
traveling
Blood Spatter Interpretation
-Origin of bloodstain
-Position of victim &
assailant
-Distance of bloodstain from
target
-Speed with which blood
left its source
-Minimum number of blows
Blood Spatter Interpretation
Blood drop characteristics:
-A free falling drop of
blood forms a sphere or
ball.
-The spherical drop will
break when it strikes
another object or when
acted upon by some force.
Blood Spatter Interpretation
-Blood droplet volume is
directly dependent upon the
surface or orifice from
which it originates.
-The impact area it strikes
is called the target.
Blood Spatter Interpretation
-The higher the height and
the faster a drop falls the
larger its diameter.
-Texture of surface changes
the shape of drop.
Blood Spatter Interpretation
Spatter size is dependent
upon velocity :
-Low Velocity
-Results from the pull of
gravity.
- Spatter is 5 ft/s & usually
3 mm or greater in diameter .
-Indication of dripping blood
Blood Spatter Interpretation
-Medium Velocity
-Results from an object as a
fist or blunt object.
-Spatter is 5 – 25 ft/s with a
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