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Forensic Serology Ch. 12. Blood Baby...cute. Nature of Blood. The word ‘blood’ refers to a highly complex mixture of cells, enzymes, proteins, and inorganic substances. Karl Landsteiner. 1901 A, B, O system of blood classification

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nature of blood
Nature of Blood
  • The word ‘blood’ refers to a highly complex mixture of cells, enzymes, proteins, and inorganic substances.
karl landsteiner
Karl Landsteiner
  • 1901
  • A, B, O system of blood classification
  • Over 100 blood factors but this, most important
  • Nobel Prize for the find!
  • Best evidence to link type to an individual or eliminate an individual
  • Comparative, identifiable evidence

The fluid portion of blood is composed principally of water.


Red blood cells (erythrocytes), white blood cells (leukocytes), and platelets are the solid materials suspended in plasma.


Antigens, usually proteins, are located on the surface of

  • red blood cells and are responsible for blood-type characteristics.
blood typing
Blood Typing
  • More than 15 blood antigen systems have been identified, but the A-B-O and Rh systems are the most important.
  • An individual that is type A has A antigens on his/her red blood cells, type B has B antigens, AB has both A and B antigens, and type O has neither A nor B antigens.

Rh factor is determined by the presence of another antigen, the D antigen.

  • People having the D antigen are Rh positive; those not having the antigen are Rh negative.

For every antigen there is a specific antibody that will react with it to form clumps known as agglutination.

  • Thus, if serum containing anti-B is added to red blood cells carrying B antigen, they will immediately react.
ratios of blood types
Ratios of Blood Types
  • O+ 1 in 3 persons
  • O- 1 in 15 persons
  • A+ 1 in 3 persons
  • A- 1 in 16 persons
  • B+ 1 in 12 persons
  • B- 1 in 67 persons
  • AB+ 1 in 29 persons
  • AB- 1 in 167 persons
  • The term serology is used to describe a broad scope of laboratory tests that use specific antigen and serum antibody reactions.

The identity of each of the four A-B-O blood groups can be established by testing the blood with anti-A and anti-B sera.

  • The concept of specific antigen-antibody reactions has been applied to immunoassay techniques for the detection of drugs of abuse in blood and urine.
  • A number of immunological assay techniques are commercially available for detecting drugs through antigen-antibody reaction.
  • In a typical EMIT analysis, antibodies that will bind to a specific drug are added to the subject’s urine.
  • Other immunoassay procedures are also available, such as radioimmunoassay (RIA) which uses drugs labeled with radioactive tags.

One such technique, the enzyme-multiplied immunoassay technique (EMIT), is used by toxicologists because of its speed and high sensitivity for detecting drugs in urine.


In the EMIT assay, a drug that may be present in a urine specimen will compete with added labeled drug for a limited number of antibody binding sites. The labeled drugs are indicated by an asterisk. Once the competition for antibody sites is completed, the number of remaining unbound labeled drug is proportional to the drug’s concentration in urine.

antigen antibody reaction
Antigen-Antibody Reaction
  • When an animal, such as a rabbit or mouse, is injected with an antigen its body will produce a series of different antibodies, all of which are designed to attack some particular site on the antigen of interest.
  • This collection of antibodies is known as polyclonal antibodies.

Alternately, a more uniform and specific collection of antibodies designed to combine with a single antigen site can be manufactured; monoclonals.


The criminalist answers the following questions when examining dried blood:

  • (1) Is it blood?
  • (2) From what species did the blood originate?
  • (3) If the blood is of human origin, how closely can it be associated to a particular individual?

Wet blood has more value than dried blood because more tests can be run.

    • For example, alcohol and drug content can be determined from wet blood only. Blood begins to dry after 3-5 minutes of exposure to air. As it dries, it changes color towards brown and black.

Blood at the crime scene can be in the form of pools, drops, smears, or crusts.

  • Pools of blood obviously have more evidentiary value in obtaining a wet sample.

Drops of blood tell the height and angle from which the blood fell. The forensic science of blood spatter analysis says that blood which fell perpendicular to the floor from a distance of 0-2 feet would make a circular drop with slightly frayed edges.


Drops from a higher distance would have more pronounced tendrils fraying off the edges (a sunburst pattern).


A blood smear on the wall or floor tells 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, or splatter. In other words, the largest area of the smear is the point of origin (a wave cast-off pattern).
  • Blood crusts need to be tested with crystalline methods to make sure it's blood.

Refrigerated red blood cells have a shelf life of about 42 days, and the serum containing white blood cells can be refrigerated up to a year. 

  • DNA can be extracted from blood (if white blood cells are present), and also from sperm, bone marrow, tooth pulp, and hair roots.
  • Blood is used in DNA testing,

as per the following steps:


1. Blood samples are collected from the victim, defendant, and crime scene2. White blood cells are separated from red blood cells3. DNA is extracted from the nuclei of white blood cells


4. A restrictive enzyme is used to cut fragments of the DNA 5. DNA fragments are put into a bed of gel with electrodes 6. Electric current sorts DNA fragments by length7. An absorbent blotter soaks up the imprint; radioactively treated, and an X-ray photograph (called an autoradiograph)

is produced 

the tests
The Tests
  • A positive result from the Kastle-Meyer color test is highly indicative of blood.
    • Hemoglobin causes a deep pink color.
  • Alternatively, the luminol test is used to search out trace amounts of blood located at crime scenes.
    • Produces light (luminescence) in a darkened area.

Microcrystalline tests, such as the Takayama and Teichmann tests, depend on the addition of specific chemicals to the blood so that characteristic crystals will be formed.

  • Precipitin test
  • Gel Diffusion
a b o vs dna
A-B-O vs DNA
  • Prior to DNA typing, bloodstains were linked to a source by A-B-O typing and the characterization of polymorphic blood enzymes and proteins.
  • DNA analysis has allowed forensic scientists to associate blood and semen stains to a single individual.
stain patterns of blood
Stain Patterns of Blood
  • The crime scene investigator must remember that the location, distribution, and appearance of bloodstains and spatters are useful for interpreting and reconstructing the events that produced the bleeding.
  • Surface texture and the stain’s shape, size, and location must be considered when determining the direction, dropping distance, and angle of impact of a bloodstain.
stain patterns of blood1
Stain Patterns of Blood
  • Surface texture is of paramount importance. In general, the harder and less porous the surface, the less spatter results.

The direction of travel of blood striking an object may be determined because the pointed end of a bloodstain always faces its direction of travel.


The impact angle of blood on a flat surface can be determined by measuring the degree of circular distortion. At right angles the blood drop is circular, as the angle decreases, the stain becomes elongated.


The origin of a blood spatter in a two-dimensions can be established by drawing straight lines through the long axis of several bloodstains.

  • The intersection or point of convergence of the lines represents the origin point.

Illustration of stain convergence on a two-dimensional plane. Convergence represents the point from which the stains emanated. Courtesy Judith Bunker, J. L. Bunker & Assoc., Ocoee, FL

categories of blood stains
Categories of Blood Stains




transfer bloodstains
Transfer Bloodstains
  • A transfer bloodstain is created when a wet, bloody surface comes in contact with a secondary surface.
  • A recognizable image of all or a portion of the original surface may be observed in the pattern, as in the case of a bloody hand or footwear.
passive bloodstains
Passive Bloodstains
  • Passive bloodstains are drops created or formed by the force of gravity acting alone.
projected bloodstains
Projected Bloodstains
  • Projected bloodstains are created when an exposed blood source is subjected to an action or force, greater than the force of gravity. (Internally or Externally produced)
  • The size, shape, and number of resulting stains will depend, primarily, on the amount of force utilized to strike the blood source.
projected bloodstains1
Projected Bloodstains
  • Arterial Spurt/Gush
    • Bloodstain pattern(s) resulting from blood exiting the body under pressure from a breached artery
  • Cast-off Stains
    • Blood released or thrown from a blood-bearing object in motion
  • Impact Spatter
    • Blood stain patterns created when a blood source receives a blow or force resulting in the random dispersion of smaller drops of blood.
    • Velocity affects stain pattern
impacted spatter
Impacted Spatter

Medium Velocity

Low Velocity

High Velocity

directionality of bloodstains
Directionality of Bloodstains
  • When a droplet of blood strikes a surface perpendicular (90 degrees) the resulting bloodstain will be circular.That being the length and width of the stain will be equal.
  • Blood that strikes a surface at an angle less than 90 degrees will be elongated or have a tear drop shape.
  • Directionality is usually obvious as the pointed end of the bloodstain ( tail ) will always point in the direction of travel.

SIN < = Width (a) 1.5cm

Length (c) 3.0cm

SIN < = 0.5

< = 30 degrees

heredity paternity
Heredity & Paternity
  • The transmission of hereditary material is accomplished by genes, located on chromosomes.
  • Alternative forms of genes that influence a given characteristic (such as eye color or blood type) are known as alleles.

Paternity testing has involved the

A-B-O blood typing system, along with blood factors other than A-B-O. Elimination or inclusion.

  • Paternity testing has implemented DNA test procedures that can establish paternity beyond 99%
testing for seminal stains
Testing for Seminal Stains
  • Some evidence sent to a

forensic laboratory involve

sexual offenses, making it

necessary to examine exhibits for the presence of seminal stains.

Who’s dress?


The best way to locate and at the same time characterize a seminal stain is to perform the acid phosphatase (an enzyme secreted into seminal fluid) color test.

testing for seminal stains1
Testing for seminal stains
  • Semen can be identified by either the presence of spermatozoa or of p30, a protein unique to seminal plasma.
  • Forensic scientists can

successfully link seminal

material to an individual by

DNA typing.


An antibody–antigen–antibody sandwich or complex is seen as a colored band. This signifies the presence of PSA in the extract of a stain and positively identifies human semen.

rape evidence
Rape Evidence
  • The rape victim must undergo a medical examination as soon as possible after the assault.
  • At that time the appropriate items of physical evidence including clothing, hairs, and vaginal and rectal swabs can be collected for subsequent laboratory examination.

All outer and undergarments should be carefully removed and packaged separately in paper (not plastic) bags.

  • Bedding, or the object upon which the assault took place, may also be carefully collected.
physical evidence from the victim
Physical Evidence from the Victim
  • Pubic combings
  • Pubic hair standard/reference sample
  • External genital dry-skin areas
  • Vaginal swabs and smear
  • Cervix swab
  • Rectal swabs and smear
  • Oral swabs & smear
  • Head hairs
  • Blood sample
  • Fingernail scrapings
  • All clothing
  • Urine specimen
rape evidence1
Rape Evidence
  • If a suspect is apprehended within 24 hours of the assault, it may be possible to detect the victim’s DNA on the male’s underwear or on a penile swab of the suspect.
  • Items routinely collected from the suspect include all clothing, pubic hair, head hair, penile swab, and a blood sample or buccal swab for DNA typing.