Who’s blood is it?
Forensic Science
T. Trimpe 2006 http://sciencespot.net/
Blood Evidence
• Blood samples – Can be analyzed to determine blood
type and DNA, which can be matched to possible
suspects.
• Blood droplets – Can be analyzed to give clues to the
location of a crime, movement of a victim, and type of
weapon.
• Blood spatter – Can be analyzed to determine
patterns that give investigators clues to how a crime
might have happened.
What makes up our blood?
• RED BLOOD CELLS (Erythrocytes) – The most abundant
cells in our blood; they are produced in the bone marrow and
contain a protein called hemoglobin that carries oxygen to our
cells.
• WHITE BLOOD CELLS (Leukocytes) – They are part of
the immune system and destroy infectious agents called
pathogens.
• PLASMA – This is the yellowish liquid portion of blood that
contains electrolytes, nutrients and vitamins, hormones,
clotting factors, and proteins such as antibodies to fight
infection.
• PLATELETS (Thrombocytes) – The clotting factors that are
carried in the plasma; they clot together in a process called
coagulation to seal a wound and prevent a loss of blood.
Blood Facts
The average adult has about FIVE liters of blood
inside of their body, which makes up 7-8% of their body
weight.
There are about one billion red blood cells in two to three
drops of blood. For every 600 red blood cells, there are
about 40 platelets and one white cell.
http://www.bloodbankofalaska.org/about_blood/index.html
Forensic Characterization
of Bloodstains
Three questions to answer:
1. Is
it blood?
2. From what species did the blood originate?
3. If the blood is human, how closely can it be
associated with a particular individual?
Kastle-Meyer Test
(phenolphthalein/peroxidase test)
when a blood stain,
hydrogen peroxide and
phenolphthalein reagent
are mixed,
Sensitivity: 1:10,000
(if 1 drop of blood were present in a
bucket with 10,000 drops of water, the
PHTH test would still turn pink)
hemoglobin - Blood contains hemoglobin
(carries oxygen and makes blood red)
which contains a heme group which
contains an Fe which can catalyze the
breakdown of hydrogen peroxide
the oxidation of the
hemoglobin in the
blood produces a
deep pink color
Forensic Characterization
of Bloodstains
Three questions to answer:
1. Is
it blood?
2. From what species did the blood originate?
3. If the blood is human, how closely can it be
associated with a particular individual?
How can a
Blood Sample
be used for
identification?
1. IS IT BLOOD?
Presumptive Tests
suggests but does not confirm the presence of
blood; indicates that other tests should be
performed
• negative result means the substance IS NOT
blood
• positive result means the substance IS LIKELY
blood (could be)
https://ecrimescenechemistrymiller.wikispaces.com/notes+on+serology
Kastle-Meyer Test
(phenolphthalein/peroxidase test)
when a blood stain,
hydrogen peroxide and
phenolphthalein reagent
are mixed,
Sensitivity: 1:10,000
(if 1 drop of blood were present in a
bucket with 10,000 drops of water, the
PHTH test would still turn pink)
hemoglobin - Blood contains hemoglobin
(carries oxygen and makes blood red)
which contains a heme group which
contains an Fe which can catalyze the
breakdown of hydrogen peroxide
the oxidation of the
hemoglobin in the
blood produces a
deep pink color
Microscopic
Views
Fish Blood
Bird Blood
Horse Blood
Frog Blood
Cat Blood
Dog Blood
Human Blood
Snake Blood
The cell membrane of RBCs has
molecules in its surface that act as
identification badges so immune
system can recognize it as a
normal component.
Normal
Red Blood Cell
ANTIBODIES
Foreign
IMMUNE
SYSTEM
CHEMICAL
MARKERS
BLOOD TYPES
Blood can be classified by either:
A. Blood Type ABO
identified by the type of antigen
(antigen A or antigen B)
B. Rhesus Factor
another type of antigen
(Rhesus positive or Rhesus negative)
So, what is an ANTIGEN?
The differences in human blood are due to
the presence or absence of certain
chemicals called antigens. Individuals have
different types and combinations of these
chemicals.
Antigen = Antibody Generating Agent
Antigens are located on the surface of the red blood
cells and the antibodies are in the blood plasma.
Blood Group A
If you belong to blood group A, you have A antigens on
the surface of your red blood cells
Blood Group B
If you belong to blood group B, you have B antigens on
the surface of your red blood cells
Blood Group AB
If you belong to blood group AB, you have both A and B
antigens on the surface of your red blood cells
Blood Group O
If you belong to blood group O, you have no antigens on
the surface of your red blood cells
Blood Group Notation
According to the above blood grouping
systems you can belong to any of the
following 8 blood groups
A Rh+
A RH-
B Rh+
B Rh-
AB Rh+
AB Rh-
O Rh+
O Rh-
Blood Typing
1. Place a drop of the blood sample in each well of the blood typing slide.
Replace the cap on the dropper vial. Note: Always replace cap before
opening next vial to prevent contamination.
2. Add a drop of anti-A (Blue) serum to the well labeled A. Replace cap.
3. Add a drop of anti-B (Yellow) to the well labeled B. Replace cap.
4. Add a drop of anti-Rh (clear) to the well labeled Rh. Replace cap.
5. Using a different color mixing stick for each well (blue for anti-A, yellow
for anti-B, white for anti-Rh), gently stir the blood sample and anti-serum
drops for 30 seconds. Discard each mixing stick after use to avoid
contamination.
6. Carefully examine the thin films of liquid mixture left behind. Observe for:
RESULT
(-) = NO
(+) = YES
Appearance
Film remains uniform in appearance
Granules present
Positive result indicates the blood type
7. Record results in the data table. Answer with a YES or NO.
Type A blood