1. Forensic Serology: Blood
Written By: Alice Yang
Period 7
Instructor Mary Villani

2. The Forensic Serologist
The forensic serologist studies body
fluids such as semen, saliva, and blood
mainly for identification purposes.
Role(s):
•Establishing type and characteristics of
blood
•Blood testing
•Examination of bloodstains
•DNA typing
•Preparation of court testimony &
evidence

3. Blood Evidence Blood is the most well-known and
significant evidence in the modern
criminal justice system.
Blood evidence is important to the forensic
investigator because:
•It can link a victim to a suspect
(Locard’s Exchange Principle]
•Bloodstain patterns can reveal a great
deal about position and movement during
the crime
•It has managed to destroy self-defense
arguments of suspects

4. Forensic Value of Blood
In forensic science, blood has always been
considered class evidence. However,
individualized blood evidence is possible
in the near future. In fact, in some cases,
forensic serologists were able to link a
single perpetrator to a bloodstain with
strong probability estimates.

5. Nature of Blood: General Characteristics
Blood is a slightly alkaline fluid that
circulates throughout our bodies,
nourishing our cells, and transporting
oxygen and waste. The fluid portion of
blood consists of plasma and serum, while
the non-fluid portion consists of red blood
cells.
Blood is composed of:
•Water
•Cells
•Enzymes
•Proteins
•Other inorganic substances

6. Nature of Blood: Serum Serum is characterized by its yellow hue,
and contains white blood cells and
platelets. Forensic analysts are able to
determine the freshness of a blood sample
by examining serum because it clots
several minutes after exposure to air. A
centrifuge can be used to separate the
clotted material from the serum portion. In
addition, serum contains antibodies ,
proteins floating in blood fluid, which have
significant forensic implications.

7. Nature of Blood: Red Blood Cells
Red blood cells, the most prevalent blood
cells in the human body, are the primary
means of delivering oxygen from the lungs
to the body’s tissues via the blood. For red
blood cells, the forensic analyst
searches for smaller chemical substances
residing on their surfaces, such as
antigens , which also tend to have
important forensic implications.

8. Blood Grouping The A-B-O system of blood typing was
discovered in 1901 by Dr. Karl Landsteiner.
During the late 1930s, a series of
antigen-antibody reactions were
discovered in blood, the most common
ones being ABH, MN, Rh, and Gm. There are
more than 256 antigens, and twenty-three
blood group systems based on association
with these antigens. A fundamental
principle of serology is that for every
antigen, there exists a specific antibody. In
fact, all blood groups are defined by the
antigens on their red blood cells and the
antibodies in their serum.

9. Blood Typing Blood typing requires two antiserums:
anti-A and anti-B. By inserting a droplet of
these antiserums in samples of blood, one
can determine which samples maintain a
normal appearance and which samples
become clotted, or agglutinated, under
microscopic examination. Type-A blood will
be agglutinated by anti-A serum; Type-B
blood will be agglutinated by anti-B serum;
Type-AB blood by both; and Type-O blood by
neither.

10. Rh Factor Blood can also be categorized using the Rh
(Rhesus disease) factor.  If an individual
has a positive Rh factor, this means that
his/her blood contains a protein that is
also found in Rhesus monkeys. 
Approximately 85% of the population has a
positive Rh factor, and doctors are trained
to monitor closely any woman who is Rh
negative and becomes pregnant. The Rh
factor, like other antigens, can be found on
the surface of red blood cells. 

11. Individualization of Blood
The potential for the individualization of
blood is based on the typing of proteins and
enzymes. Blood proteins and enzymes have
the quality of being polymorphisms or
iso-enzymes , which means they exist in
several forms and variants. Most people
are familiar with at least one common
polymorphism in blood: Hb, which causes
sickle-cell anemia.

12. Secretors In 1925, a blood-related discovery valuable
to forensic science was made.
Approximately eighty-percent of the human
population was found to be "secretors,"
individuals whose specific types of
antigens, proteins, antibodies, and
enzymes characteristic of their blood can
be found in other bodily fluids and
tissues.  In the case of a secretor,
investigators can conclude the blood type
by examining the saliva, teardrops, skin
tissue, urine, or semen. In a rape case, for
example, where the perpetrator is a
secretor, potential suspects can be
narrowed down through blood type
analysis.

13. Bloodstain Analysis: The General Questions
During bloodstain analysis, the forensic
investigator uses these five specific
questions as guidelines for determining
the nature of a crime.
1. Is the sample blood?
2. Is the sample animal blood?
3. If the sample is animal blood, from what
species did it come from?
4. If the sample is human blood, what type
is it?
5. Can the sex, age, and race of the source
of blood be determined?

14. Bloodstain Analysis: Blood or not?
To determine whether or not blood is
present at a crime scene, forensic
investigators use color or crystalline tests.
In the past, police investigators were
trusted to verify the presence or absence of
blood, but Miller v. Pate (1967) enforced that
physical tests should be completed in the
search for blood. The Benzidine test was
widely implemented until it was discovered
to be a known carcinogen. The current
Kastle-Meyer test, which uses the
chemical, phenolphthalein, operates on the
fact that when phenolphthalein comes in
contact with hemoglobin, it releases
peroxidase enzymes that cause a bright
pink color to appear. 

15. Bloodstain Analysis: Blood or not?
In order to detect invisible bloodstains,
forensic investigators use the luminol test.
Luminol, a chemical sprayed on carpets
and furniture, reveals a slightly
phosphorescent light in the dark where
bloodstains (and other stains) are present.
Long-dried blood has a tendency to
crystallize, or can be made to crystallize
with various saline-acid mixtures. The
names of various crystal tests are the
Teichman test , the Takayama test , and
Wagenhaar test. 

16. Bloodstain Analysis: Animal Blood?
To determine whether blood at the crime
scene originated from an animal, forensic
investigators use antiserum or gel tests.
Establishing whether or not blood is animal
blood is significant because any possibility
of an injury to the household pet, caused by
a perpetrator or another animal, must be
eliminated. Pets generally spread human
bloodstains throughout the crime scene,
but the pet can be a victim, perpetrator, or
witness (through the cross transfer of
evidence between the animal’s DNA and the
perpetrator). Veterinary forensics may be a
necessary unit if pets are involved in the
crime.

17. Bloodstain Analysis: Animal Blood?
To determine whether blood is animal or
human in origin, the precipitin test is
conducted. This process involves injecting
an animal, usually a rabbit, with human
blood. The rabbit's body creates
anti-human antibodies, which are then
extracted from the rabbit's serum. If this
antiserum is then placed on a sample from
the crime scene, and the blood displays
clotting, the forensic investigator can
conclude that the blood is human blood.
The same procedure of creating and
extracting antiserum can be applied to
every known animal.

18. Bloodstain Analysis: Human Blood?
To confirm whether blood is human in
origin, the forensic investigator must first
determine that he has an adequate and
quality blood sample. A blood sample that
meets these requirements can undergo
direct typing using the A-B-O system. If
severely dried stains are uncovered,
indirect typing should be completed using
techniques such as the absorption-elution
test. During this test, the forensic scientist
adds compatible antiserum antibodies to a
sample, heats the sample to break the
antibody-antigen bonds, and finally inserts
known red blood cells from standard blood
groups to see what coagulates.

19. Bloodstain Analysis: Age, Sex, & Race
To estimate the age, sex, and race using
blood found at the crime scene, the
forensic scientist uses various color and
nitrate tests, and applies heredity
principles to his tests. Unfortunately, no
exact determinations are possible.
However, clotting and crystallization can
help approximate age, testosterone and
chromosome testing can help determine
sex, and certain racial genetic markers
involving protein and enzyme tests can
help establish race.

20. Blood & Crime Scene: Wet vs. Dry Blood
Wet blood is more significant than dried
blood because the forensic scientist can
perform more tests in order to gain insight
to the happenings of the crime. For
example, alcohol and drug content can be
determined from wet blood only. Blood
begins to dry after three to five minutes of
exposure to air. As it dries, it changes color
from a deep red towards brown and black.
Blood can be categorized into pools, drops,
smears, or crusts.

21. Projection of Blood Forensic investigators can determine how
blood was projected from the body by
examining factors such as:
Type of injuries
The order in which the wounds were received
Whose blood is present
The type of weapon that caused the injuries
Whether the victim was in motion or lying still when the injury was inflicted
Whether the victim was moved after the injury was inflicted
How far the blood drops fell before hitting the surface where they were found.

22. Blood & Crime Scene: Categories of Blood Patterns
Pools of blood have evidentiary value in
collecting a wet sample. Drops of blood can
reveal the height and angle from which the
blood fell onto the surface. According to
forensic scientists, the blood spatter
analysis claims that blood which falls
perpendicular to the floor from a distance
of zero to two feet would create a circular
drop with slightly frayed edges. Drops from
a higher distance would have more distinct
tendrils extending off the edges.

23. Blood & Crime Scene: Categories of Blood Patterns
A blood smear on the wall or floor can
indicate the direction of force of the
blow.  The direction of force is always in the
direction towards the tail, or smaller end, of
the smear. In other words, the largest area
of the smear is the point of origin. Blood
crusts must be tested with crystalline
techniques to verify that they are actually
blood. Refrigerated red blood cells have a
shelf life of about forty-two days, and the
serum containing white blood cells can be
refrigerated much longer, almost up to a
year.  DNA can be extracted from blood (if
white blood cells which always contain a
nucleus are present), and also from sperm,
bone marrow, tooth pulp, and hair roots.

24. Blood & DNA Testing Blood is used in DNA testing, as shown by
the following steps:
1. Blood samples are collected from the
victim, defendant, and crime scene.
2. White blood cells are separated from red
blood cells.
3. DNA is extracted from the nuclei of white
4. A restrictive enzyme is used to cut
fragments of the DNA strand.
5. DNA fragments are put into a bed of gel
with electrodes at either end.
6. Electric current sorts DNA fragments by
length.
7. An absorbent blotter soaks up the imprint; it
is radioactively treated, and an X-ray
photograph, called an autoradiograph, is
produced.

25. Blood & Crime Scene Regardless of what type of analysis is used
on the blood at the crime scene, care must
be taken to handle it properly and to
prevent putrefaction.  Photographs and
notes should be taken before any blood is
lifted.  Samples should not be exposed to
heat, moisture, or bacterial contamination,
because these factors can shorten the
survival time of proteins, enzymes, and
antigens.  Delays in bringing samples to the
lab must be avoided at all cost, because it
can diminish evidential value.

26. Court Significance Experts in bloodstain examination are
usually law enforcement personnel. In
certain jurisdictions, a police investigator
or blood specialist may testify on the core
issue because blood evidence is usually a
vital aspect of the crime scene.
An expert in bloodstain examination has:
•Completed specialized training
•Conducted a sufficient number of
examinations
•Accumulated enough reference patterns
to reinforce an argument

27. References
Data
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28. References Slide 6: http://www.antibody.com/images/CD4.gif

29. References
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