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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. Objectives, continued.

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Presentation Transcript

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.

objectives continued
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.

Serology is the examination and analysis of body fluids.

A forensic serologist may analyze a variety of body fluids including saliva, semen, urine, and blood.

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.

blood characteristics
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.

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.

Composition of 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.

Historical Perspective of Blood Typing
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

Blood Terminology
unknown stain at a scene
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

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 blue-green color

Luminol test—reaction with blood to produce light

Presumptive Tests for Blood Determination

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.

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.

Human versus Animal Blood
animal blood
Animal Blood

Larger nucleic red blood cells

Frog blood

human 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.

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.

Blood Typing—Proteins
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.

Blood Typing
blood groups
Blood Groups

Can Give

Blood To

Can Get

Blood From




O, A









O, B


A nor B


A, B, O, AB


A and B


A nor B

A, B, O, AB

A and B



why is blood typing important to forensic science
Why is blood typing important to forensic science?
  • 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.

BTW: When packaging and storing blood evidence, do not block out air (no sealed containers). Use a paper bag or envelope.

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.

Blood Typing—Probability and Blood Types
blood typing antibodies additional proteins and enzymes
Antibodies are proteins secreted by 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.

Blood Typing—Antibodies; Additional Proteins and Enzymes
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 antigen-antibody 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.

Key Points
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.

Basics of 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.

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.Secretors
blood pattern reconstruction
Scene Pattern Reconstruction

1. Stain condition

2. Pattern

3. Distribution

4. Location

5. Directionality

Lab Results Reconstruction

1. Genetic marker typing

2. Age determination

3. Source determination

4. Race determination

5. Sex determination

Blood Pattern Reconstruction

—From Cracking Cases by Dr. Henry C. Lee and Thomas W. O’Neil

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.

Blood Spatter Evidence
people of historical significance
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.

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?

Blood Droplet Characteristics
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.

Blood Droplet Volume
conditions affecting shape of blood droplet
Size of the droplet

Angle of impact

Velocity at which the blood droplet left its origin


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

Conditions Affecting Shape of Blood Droplet
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

Questions Answered by Blood Spatter Interpretation
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.

Blood Spatter Analysis
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


Cast-off—blood that is thrown from an object in motion

Bloodstain Terminology
bloodstain terminology continued
Contact stain—bloodstains caused by contact between a wet blood-bearing surface and a second surface that may or may not have blood on itBloodstain Terminology, continued
  • 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

blood spatter analysis six patterns
Describe each of these:

a. passive drops

b. arterial gushes

c. splashes

d. smears

e. trails

f. pools

Blood Spatter Analysis—Six Patterns
bloodstain terminology continued1
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.

Bloodstain Terminology, continued
  • 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
bloodstain patterns
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:

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?

Blood Spatter Analysis—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.

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?

Blood Spatter Analysis—Directionality
bloodstain patterns1
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.

area of intersection and convergence
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.

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.

Blood Spatter Analysis—Location of the Origin of the Blood
crime scene investigation of blood
Search for blood evidence.

If any is discovered, process it determining:

Whether the evidence is blood.

Whether the blood is human.

The blood type.

Interpret the findings:

See if the blood type matches a suspect.

If it does not, exclude that suspect.

If it does, decide if DNA profiling is needed.

Crime Scene Investigation of 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.

Blood Evidence
people in the news
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.

more about serology
More about Serology

For additional information about blood evidence, and famous crimes that involve serology, check out truTV’s Crime Library at: