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Blood
Forensic Serology and Blood Spatter Analysis
Blood
• A complex fluid that consists of two
portions:
– Cellular elements – Red Blood
Cells, White Blood Cells and
Platelets
– Plasma (or serum) – liquid portion
of the blood which contains
dissolved substances
Red Blood Cells - Erythrocytes
• Small, biconcave discs with
no nucleus
• 5 million per cubic ml.
• Carry oxygen and carbon
dioxide using red pigment
(hemoglobin)
• Live for about 120 days, then
are removed by the liver or
engulfed by white blood
cells
White Blood Cells - Leukocytes
• Larger than RBC’s and have
nuclei (which may be fragmented
as in this neutrophil)
• Function as the immune system –
destroy foreign cells
• Many different types and names
(eg. Monocytes, macrophages,
lymphocytes, T cells,B cells, etc.)
Platelets
Thrombocytes
• Tiny cellular fragments with no nuclei
• Formed in bone marrow with WBC’s and
RBC’s
• Contain proteins that are released when a
wound occurs to initiate the process of blood
clotting
Bone Marrow
• Located within the large
bones (especially the leg
bones and pelvis) is a tissue
that produces all three types
of blood cells
• Since RBC’s and platelets
cannot reproduce, without
functioning bone marrow we
would soon die
Plasma
• The composition of whole blood
varies – but if centrifuged it
consists of mostly plasma
• This liquid contains many
important proteins (like antibodies,
hormones, carrier molecules) that
are essential to proper body
functioning
• Plasma is about 90% water, 7-9%
protein and also contains glucose
and other nutrients, waste
products, dissolved gases etc.
Blood Testing
• A great deal can be learned about a person and/or
their circumstances with the proper blood test
• Since there are dozens of even routine tests, the
key in forensics is to order the proper test
• Standard tests like the CBC (complete blood cell)
can reveal large changes in blood composition
• Changes in blood enzyme levels can be detected
when tissue (like heart) is damaged
• Changes in levels of some proteins in the blood
can signal cancer, or liver disease, etc.
Some disorders seen with
a simple blood test
Sickle Cell
Anemia
Identification of Blood
• Forensic investigators often want to know whose
blood they have collected from the crime scene
• Several methods have been devised, but all involve
the immune system
• Blood typing was first done by Karl Landsteiner in
1901
• Transfusions became safer, and some degree of
identity was assigned to blood
• Presently DNA fingerprinting is the gold standard
for identifying blood (covered later)
Blood Types
• The ABO system relies on antigens – proteins
on the outer membrane of RBC’s
• There are only two types of these proteins in
this blood system: A and B
• Cells can have only A antigens(Type A), only
B antigens (Type B), both A and B antigens
(Type AB) and no antigens for this system
(Type O)
Blood Types
• If a person does NOT normally
produce an antigen, they can make
antibodies against that foreign
antigen
• These antibodies will clump
(agglutinate) the blood cells
together and make it impossible
for proper circulation to occur
• In the lab, these antibody reactions
are used to type blood
Agglutinated
vs.
Normal
Blood Types
Blood Types
• Sera are produced that contain anti-A and anti-B
antibodies (horses)
• These sera are applied to blood on a plate
• Blood type A will agglutinate when exposed to anti-A
serum, blood type B will agglutinate when exposed to
blood type B serum
• What will blood types AB and O do when exposed to
the sera?
Blood Types
In North America a
typical distribution
of blood types
• Matching one of only 4 types is less than
definitive
• Before DNA testing, 5 or 6 blood typing
systems were used to further identify the
blood
Immunoassays
• Many drug tests now use the immune system
• Antibodies can be produced in animals (harmless)
by first combining the drug with a protein and
injecting it into the animal
• The animal will produce antibodies to the drug
• These antibodies can be removed from the animal,
purified, and used in tests to detect the drug
EMIT Test
• A typical immunoassay for drugs
• Add antibodies to a blood or urine sample
• Any drug present (eg. Heroin) will bind to the
antibodies
• Then, enzyme labeled drug is added to the urine
• The quantity of enzyme-labeled heroin left over is
measured and this value is related to the
concentration of the drug in the sample
• Caution is needed since it is possible that the
antibodies can combine with related drugs –
positive results must be confirmed with other tests
Blood Stains
Finding Blood
• In some cases, blood will be obvious at the
crime scene
• In others, the perpetrator may have tried to
clean up the blood
• Often this blood can be visualized using a
number of methods
The Kastle-Meyer Test
• Used to use benzidine (carcinogenic), now uses
phenolphthalein – turns deep pink when exposed
to hemoglobin
• Not specific for hemoglobin – some vegetable
substances like potatoes and horseradish may test
positive
• Also, Hemastix® – usually used as dipsticks for
urine testing – are convenient tests for trace
amounts of blood
Luminol
• Luminol reagent is sprayed
onto surface
• Region is darkened,
luminol glows
• Can detect bloodstains
diluted up to 10 000 times
• does not interfere with
future DNA tests
Precipitin Test
• Precipitin tests rely on antisera produced
in much the same way as for
immunoassays
• Whole human blood is injected into the
animal (or animal blood)
• Antibodies are extracted and used to react
with the blood stain to determine if it is
human blood
• Very sensitive – can detect bloodstains
even 15 years old or older (even
mummies!)
• Three methods of visualizing results are
used: capillary tube method, gel diffusion,
and electophoretic method
Capillary Tube Precipitin Test
Extract of bloodstain
layered on antiserum
to human blood
Cloudy ring between
layers indicates a
reaction – thus the
blood is human
Gel Diffusion
Precipitin Test
Bloodstain and human antiserum placed in
different wells on an agar plate
Antigen and antibody, if matched, will tend to
diffuse toward each other
Line of precipitation can be seen – positive test
for human blood
Electrophoretic method is similar – uses
electricity to draw antigens and antibodies through
the gel
Typing of Dried Stains
• Although it is possible to determine if there
is blood present and if it is human when dry,
typing is not possible because the RBC’s
rupture
• Procedures to type dry blood have been
developed, but have largely been replaced
now with DNA fingerprinting technology
Stain Patterns of Blood
Surface Texture
• Surface is extremely important to the
interpretation of bloodstain evidence
• In general, the harder and less porous the
surface, the less spatter results
• Control experiments on identical (or
similar) surfaces must be conducted to
determine distance of spatter, direction, etc
Direction of Travel
• The blood’s direction
of travel can be
determined by the
stain’s shape
• The pointed end of a
bloodstain always
faces its direction of
travel
Impact Angle
• The degree of circular distortion is an
indicator of the angle of the trajectory of
the blood before it hit the object
• As the angle increases, the stain becomes
more elongated
Effect of Gravity
The position of an object when blood hit it can be
determined by the effect of gravity on the blood
drop after it contacts the surface
Here, the effect of
arterial spurting are
noted
Large drops
indicate blood loss
was severe
A cut carotid
artery could
easily
produce the
volumes of
blood seen in
the previous
photo
Insect Transfer of Blood
It is possible that flies may gorge themselves on blood at a
crime scene and subsequently regurgitate the blood
This may give investigators an inaccurate view of the
location of the bloodshed
Investigators must be aware of such a possibility and take
this into account when seeing seemingly unexplainable
patterns
Origin of the Blood
• The site of origin of the blood can often be
determined by drawing straight lines
through the long axis of several individual
bloodstains
• The intersection or point of convergence or
the lines represents the point from which the
blood emanated
Other Body Fluids- Semen
• Another body fluid often searched for in cases of
rape is semen
• Semen is the fluid ejaculate that contains sperm and
other secretions
• Acid phosphatase is an enzyme present in large
amounts in semen
• MUP (4-methyl umbelliferyl phosphate) will
flouresce under UV light when it comes in contact
with acid phosphatase
• Used to search large areas (bedsheets, carpets, etc.)
Other Body Fluids - Semen
• Also, soaking material in
water and then
examining the water may
reveal the presence of
sperm
• Many men have had
vasectomies, so sperm
are not always present
Summary
• Blood testing (serology) can reveal many details
about the owner including the presence of disease,
toxins, and cell damage
• The immune system is used to test blood for type
and for drugs
• Blood stains, even if old or cleaned can be
detected and tested
• Blood spatter patterns often reveal information
about the whereabouts of the victim and/or
perpetrator during the crime
THE END