Transcript Forensic Serology - North Salem Schools Teachers Module

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