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Blood
Blood
Objectives
You will understand:
That an antibody and an antigen of
different types will agglutinate, or
clump, when mixed together.
That the significance of the evidence
depends on a characteristic’s
relative occurrence in the
population.
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Blood
Objectives, continued
You will be able to:
Determine whether a stain is blood.
Determine whether a bloodstain is
human or animal blood.
Determine the blood type of a
simulated bloodstain using the
ABO/Rh system.
Explore bloodstain patterns as a
function of velocity, direction, and
height of fall.
Use technology and mathematics to
improve investigations and
communications.
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Blood
Serology
 Serology is the examination and analysis of body fluids.
1. A forensic serologist may analyze a variety of body fluids including saliva, semen,
urine, and blood.
2. From 1950 to the late 1980s, forensic serology was a most important part of lab procedures.
With the development of DNA techniques, more time, money, and significance were placed
on developing DNA labs. However, with limited funds and the time required for DNA testing,
most labs still use many of the basic serology testing procedures.




Blood typing can provide class evidence; whereas DNA profiling can
provide individual evidence.
A blood spatter pattern can give information about the truthfulness of an
account by a witness or a suspect.
It also can provide information about the origin of the blood, the angle and
velocity of impact, and type of weapon used.
Our understanding of blood began in ancient times and continues to grow
today.
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Blood
Blood Characteristics
Plasma is the fluid portion of the blood (55
percent).
Cells (45 percent)
Erythrocytes are red blood cells. They
are responsible for oxygen
distribution.
Leukocytes are the white blood cells;
they are responsible for “cleaning”
the system of foreign invaders.
Thrombocytes or platelets are
responsible for blood clotting.
Serum is the liquid that separates from the
blood when a clot is formed.
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Blood
Composition of Blood
 Whole blood carries cells and plasma—the fluid with
hormones, clotting factors, and nutrients.
Shown above respectively:
 Red blood cells carry oxygen to the body’s cells and carbon
dioxide away.
 White blood cells fight disease and foreign invaders and, alone,
contain cell nuclei.
 Platelets aid in blood clotting and the repair of damaged blood
vessels.
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Blood
Historical Perspective of Blood Typing
Around 1900, Karl Landsteiner discovered that there are four
different types of human blood based on the presence or
absence of specific antigens found on the surface of the red
blood cells.
In 1940, Landsteiner and Weiner reported the discovery of the Rh
factor by studying the blood of the Rhesus monkey. 85 percent
of Caucasians, 94 percent of Black Americans, and 99 percent
of all Asians are Rh positive.
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Blood
Blood Terminology
ABO blood groups—based on having A, B, both, or no antigens on
red blood cells
Rh factor—may be present on red blood cells; positive if present and
negative if not
Antigen—a substance that can stimulate the body to make antibodies.
Certain antigens (proteins) found in the plasma of the red blood
cell’s membrane account for blood type.
Antibody—a substance that reacts with an antigen
Agglutination—clumping of red blood cells; will result if blood types
with different antigens are mixed
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Blood
Unknown Stain at a Scene
Questions to be answered:
Is it blood?
Is it human blood?
Whose is it?
Determine blood type, alcohol content,
drugs present
Determine the method(s) in which
blood may have been deposited
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Blood
Presumptive Tests for Blood Determination
Kastle-Meyer color test—a mixture of phenolphthalein and hydrogen
peroxide; the hemoglobin will cause the formation of a deep pink
color if blood is present
Hematest tablet—reacts with the heme group in blood, causing a bluegreen color
Luminol test—reaction with blood to produce light
Luminol is the most sensitive chemical test that is capable of presumptively detecting
bloodstains diluted up to 300,000 times. Its reaction with blood emits light and thus
requires the result to be observed in a darkened area.
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Blood
Human versus Animal Blood
Microscopic observation
Precipitin test—blood is injected into a rabbit; antibodies are formed; the
rabbit’s blood is extracted as an antiserum; the antiserum is placed on
sample blood. The sample will react with human proteins if human
blood is present. This test is very sensitive and requires only a small
amount of blood.
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Blood
Animal Blood
Larger nucleic red blood cells
Frog blood
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Blood
Human Blood
Red blood cells are most
numerous; 5 to 6 million per
mm3
White blood cells are larger and
less numerous; 5,000 to
10,000 per mm3
Platelets are tiny, cellular
fragments; 350,000 to 500,000
per mm3
The average adult carries 4 to 5 L
of blood.
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Blood
Blood
Typing—
Proteins
42%
12%
3%
43%
of the population in the United States
(of which 85% is Rh+)


Blood typing is quicker and less expensive
than DNA profiling.
It produces class evidence but can still link a
suspect to a crime scene or exclude a suspect.
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Blood
Blood Typing
Blood type A has antigen A on the surface of the cell and will
agglutinate with blood type B.
Blood type B has antigen B on the surface of the cell and will
agglutinate with blood type A.
Blood type AB has antigens A and B on the surface of the cells and
will not agglutinate with either type A or type B blood.
Blood type O has neither antigen A nor B and will not agglutinate.
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Blood
Blood Groups
Type
Antigen
Antibody
Can Give Can Get
Blood To Blood From
A
A
B
A, AB
O, A
B
B
A
B, AB
O, B
AB
A and B
Neither
A nor B
AB
A, B, O, AB
O
Neither
A nor B
A and B
A, B, O, AB
O
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Blood
Population Distribution of Blood Types in the
U.S.
Type
Percent
O
45
A
40
B
11
AB
4
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Blood
Why is blood
typing important
to forensic
science?
BTW: When packaging and storing blood
evidence, do not block out air (no sealed
containers). Use a paper bag or
envelope.
 What is probability of a
person having B+ blood?
 11/100 x 85/100 =
935/10,000 or about 1
out of 10 people.
 Calculate the probability
of having AB- blood.
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Blood
Blood Typing—Probability and
Blood Types
 Given the frequency of different genes within a
population, it is possible to determine the
probability that a particular blood type will appear in
a particular population.
 To determine the probability of two separate
events, it is necessary to multiply their individual
probabilities.
 By identifying the additional proteins in the blood
evidence sample, investigators can limit the size of
a suspect population and help identify a suspect.
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Blood
Blood Typing—Antibodies;

Additional
Proteins
and
Antibodies are proteins
secreted by
Enzymes
white blood cells
that attach to antigens
to destroy them.
 Antigens are foreign molecules or cells
that react to antibodies.
 Enzymes are complex proteins that
catalyze different biochemical reactions.
 Many enzymes and proteins have been
found in the blood that are important for
identification purposes.
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Blood
Key Points
 Serology involves a broad scope of lab tests that
use specific antigen and serum antibody reactions.
 An antibody reacts or agglutinates only with its
specific antigen. The concept of specific antigenantibody reactions has been applied to techniques
for detecting drugs in blood and urine.
 Every red blood cell contains either an A antigen, a
B antigen, or no antigen (this is called type O). The
type of antigen on one’s red blood cells determines
one’s ABO blood type.
 The determination of blood is best made with a
preliminary color test. Review the presumptive tests.
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Blood
Basics of Heredity
 The gene is the basic unit of heredity. A
chromosome is a threadlike structure in the cell
nucleus, along which the genes are located.
 Most human cells contain 46 chromosomes (23
mated pairs). Egg and sperm contain 23 unmated
chromosomes.
 An allele is any of several alternative forms of genes
that influence a given characteristic and that are
aligned with one another on a chromosome pair.
 A heterozygous gene pair is made up of two
different alleles. A homozygous gene pair is made
up of two similar alleles.
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Blood
Heredity
 When two different genes are inherited, the
characteristic coded for by a dominant gene is
expressed. The characteristic coded for by a
recessive gene remains hidden.
 A genotype is the particular combination of genes
present in the cells of an individual. A phenotype is
the physical manifestation of a genetic trait.
 Type A blood (phenotype) can be AA (homozygous
genotype) or AO (heterozygous genotype). Type B
blood can be BB or BO. Type AB blood is only AB
genotype. Type O blood is only OO genotype.
 Review how to do Punnett squares with blood types
to determine parent/offspring relationships.
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Blood
Secretors
80% of the population are secretors.
Their blood-type antigens are found in
high concentration in their body fluids
such as saliva, semen, vaginal
secretions and gastric juice.
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Blood
Blood Pattern Reconstruction
Scene Pattern
Reconstruction
Lab Results
Reconstruction
1. Stain condition
1. Genetic marker typing
2. Pattern
2. Age determination
3. Distribution
3. Source determination
4. Location
4. Race determination
5. Directionality
5. Sex determination
—From Cracking Cases by Dr. Henry C. Lee and
Thomas W. O’Neil
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Blood
Blood Spatter Evidence
A field of forensic investigation that deals with the physical
properties of blood and the patterns produced under different
conditions as a result of various forces being applied to the
blood.
Blood, as a fluid, follows the laws of physics.
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Blood
People of Historical Significance
Paul Kirk (1902–1970) was a professor of criminalistics and
biochemistry at the University of California at Berkeley. He
actively assisted law enforcement organizations from 1935 to
1967. His book Crime Investigation contained a chapter in which
he discussed the application of bloodstain pattern analysis to
criminal investigations. Dr. Kirk analyzed the bloodstain pattern
photos from the Sam Sheppard case and was instrumental in
Sheppard’s release after his second trial. Find out more about the
case at truTV’s Crime Library.
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Blood
Blood Droplet Characteristics
 A blood droplet remains spherical in space until it collides with a
surface.
 Once a blood droplet impacts a surface, a bloodstain is formed.
 Droplets falling from the same height, hitting the same surface at
the same angle, will produce stains with the same basic shape.
 How will the shape change as the height is increased or
decreased?
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Blood
Blood Droplet Volume

A droplet contains approximately 0.05 cc of fluid.

Is not the same for all blood droplets, but is generally from 0.03 cc
to 0.15 cc

Is directly dependent upon the surface or orifice from which it
originates

The impact area is called the target.
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Blood
Conditions Affecting Shape of Blood Droplet
Size of the droplet
Angle of impact
Velocity at which the blood droplet left its origin
Height
Texture of the target surface
• On clean glass or plastic—droplet will have smooth outside edges
• On a rough surface—will produce scalloping on the edges
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Blood
Questions Answered by Blood
Spatter Interpretation
The distance between the target surface and the origin of the
blood
The point(s) of origin of the blood
Movement and direction of a person or an object
The number of blows, shots, etc., causing the bloodshed and/or
the dispersal of blood
Type and direction of impact that produced the bloodshed
The position of the victim and/or object during bloodshed
Movement of the victim and/or object after bloodshed
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Blood
Blood Spatter
Analysis
 When blood falls from a height or at a high
velocity, it can overcome its natural
cohesiveness and form satellite droplets.
 When it falls onto a less-than-smooth surface,
it can form spiking patterns around the
drops.
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Blood
Bloodstain Terminology
Angle of impact—angle at which blood strikes a target surface
Bloodstain transfer—when a bloody object comes into contact with a
surface and leaves a patterned blood image on the surface
Backspatter—blood that is directed back toward the source of
energy
Cast-off—blood that is thrown from an object in motion
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Blood
Bloodstain Terminology, continued
Contact stain—bloodstains caused by contact between a wet bloodbearing surface and a second surface that may or may not have blood
on it
• Transfer—an image is recognizable and may be identifiable
with a particular object
• Swipe—wet blood is transferred to a surface that did not
have blood on it
• Wipe—a non-blood-bearing object moves through a wet
bloodstain, altering the appearance of the original stain
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Blood
Blood Spatter Analysis—Six
Patterns
Describe each of these:
a. passive drops
b. arterial gushes
c. splashes
d. smears
e. trails
f. pools
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Blood
Bloodstain Terminology, continued
Directionality—relates to the direction a drop of blood travels in
space from its point of origin
Terminal velocity—the greatest speed to which a free-falling drop of
blood can accelerate in air. It is dependent upon the acceleration of
gravity and the friction of the air against the blood—approximately
25.1 feet/second.
• High velocity—greater than 25 feet per second, usually
100 feet per second; gives a fine mist appearance
• Medium velocity—5 to 25 feet per second
• Low velocity—5 feet per second or less
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Blood
Bloodstain Patterns
The shape of a blood drop:
Round—if it falls straight down at a 90-degree angle
Elliptical—blood droplets elongate as the angle decreases from 90
to 0 degrees; the angle can be determined by the following
formula:
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Blood
Blood Spatter Analysis—Impact
Patterns can help investigators determine the
type of weapon used.
 What kind of a pattern is produced by a gun
shot?
 What kind of a pattern is produced by a
hammer blow?
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Blood
Impact
The more acute the angle of
impact, the more elongated the
stain.
90-degree angles are perfectly
round drops; 80-degree angles
take on a more elliptical shape.
At about 30 degrees the stain will
begin to produce a tail.
The more acute the angle, the easier it is to determine the
direction of travel.
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Blood
Blood Spatter Analysis—
Directionality
The shape of an individual drop of blood
provides clues to the direction from where
the blood originated.
How will the point of impact compare with the
rest of a blood pattern?
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Blood
Bloodstain Patterns
The harder and less porous the
surface, the less the blood drop
will break apart.
The softer and more porous the
surface, the more the blood
drop will break apart.
The pointed end of the bloodstain
faces the direction of travel.
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Blood
Area of Intersection and Convergence
The location of the blood source can
be determined by drawing lines
from the various blood droplets to
the point where they intersect.
The area of convergence is the point
of origin—the spot where the
“blow” occurred. It may be
established at the scene by
measurement of angles with the
use of strings.
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Blood
Blood Spatter Analysis—Location of
the Origin of the Blood
Lines of convergence
 Draw straight lines down the axis of the
blood spatters.
 Where the lines converge, the blood
originated.
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Blood
Crime Scene Investigation of Blood
Search for blood evidence.
2. If any is discovered, process it determining:
a. Whether the evidence is blood.
b. Whether the blood is human.
c. The blood type.
3. Interpret the findings:
a. See if the blood type matches a suspect.
b. If it does not, exclude that suspect.
c. If it does, decide if DNA profiling is needed.
1.
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Blood
Blood Evidence
Class evidence for blood includes blood type. If you can determine
the DNA, you will have individual evidence.
Bloodstain patterns are considered circumstantial evidence in a
courtroom. Experts can argue many points, including direction of
travel, height of the perpetrator, position of the victim, left/right
hand, whether the body was moved, etc.
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Blood
People in the News
Herbert L. MacDonell is considered by many to be the father of
modern bloodstain pattern analysis. He is the director of the Lab
of Forensic Science and founder of the Bloodstain Evidence
Institute (1973) in Corning, NY. His book Bloodstain Pattern
Interpretation helped to jump-start this discipline. He has
consulted on criminal cases in all 50 states, in addition to
testifying in the O. J. Simpson trial and in the assassination cases
of Sen. Robert F. Kennedy and
Dr. Martin Luther King, Jr.
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Blood
More about Serology
For additional information about blood evidence, and famous
crimes that involve serology, check out truTV’s Crime Library at:
www.crimelibrary.com/criminal_mind/forensics/serology/1.html
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