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CPU-Net MEDICAL
ALERT
A Bi-Monthly Bulletin Published by the Child Protection Unit Network
Jan – Feb 2005
Vol. 3 Issue 1
BLOOD TYPING: In Or Out As Evidence?
A single blood-trace can provide a wealth of information in
crime investigations. A bloodstain in a crime scene always links
the suspect and victim to one another and the scene of violence.
Blood and tissue forced under the fingernails of the victim during a
violent struggle can also be linked to the assailant. There are
specific steps in analyzing blood stains and analytical techniques
have improved that would help narrow down suspects. For
example, traces of drugs found in a bloodstain indicate medical
treatment which a person might be receiving.
Nevertheless, forensic serology is important not only for
narrowing suspicion on the guilty but also in showing a suspect's
innocence. Blood typing is a mere part of forensic serology but
has been traditionally used in excluding suspects in certain cases.
However, as this CPU-Net MEDICAL ALERT would show,
blood typing has its limitations and may not be reliable even as a
tool for excluding suspects.
When suspicious stains are found in a crime scene or on a
victim, the following are questions and tasks done by a forensic
serologist:
1. Is the sample blood?
The first task in examining suspicious stains is to determine
whether they are blood. A number of substances such as fruitstains or dye may soil clothing and take on the appearance of
bloodstains.
The benzidine test is used for many years but has been
discontinued because the reagent is carcinogenic. At present, the
Kastle-Meyer test is used to confirm the presence of blood. The
test uses phenolphthalein solution, which turns pink in contact
with even small traces of blood. The test works by detecting the
presence of the enzyme peroxidase in the blood. However, this
substance is also present in other biological materials, such as
potato and horseradish. Thus, the Kastle-Meyer test is regarded
as a screening procedure. It is a highly sensitive test and a
positive reaction is judged presumptive of blood. Further
confirmatory tests are then carried out. These are usually
chemical and microscopic procedures to identify blood by its
pigments and cellular structures.
2. What if there are no detectable bloodstains?
To detect invisible bloodstains, the luminol test is used,
which is a chemical sprayed on carpets and furniture. This would
reveal a slight phosphorescent light in the dark where bloodstains
(and certain other stains) are present.
3. Is the sample animal blood? If it is animal blood, from
what species?
Once a stain has been confirmed as blood, it has to be
determined whether it is human or animal using the precipitin
test. Blood of every animal species contains different proteins,
and blood from one species will develop antibodies from another
species as a protective measure against disease and foreign
matter.
This principle is used to test whether bloodstains are human
or not. Serum for the precipitin test is obtained from rabbits which
have produced antibodies to destroy a small quantity of human
blood injected into them. A drop of this anti-human serum is
added to suspect blood, which will precipitate its protein if it is of
human origin. Police laboratories hold anti-sera for most common
animals, thus allowing the crime investigator to confirm or
disprove statements made by the suspects about the origin of
suspicious bloodstains. The precipitin test is sensitive, and will
work on small traces of blood. The test is also known as the
Uhlenbuth test after the German scientist who developed it in
1901.
You may ask, “Why is it important to test for animal blood?”
The answer is that any possibility of an injury to the household pet
must be ruled out (or a fight between two pets, if pets are
present). Pets normally spread human bloodstains all around the
crime scene, but the pet can be a victim, perpetrator, or witness
(by the transfer of animal DNA to the perpetrator).
4. If it is human blood, what is the blood group or type?
To determine the blood type, forensic scientists must first
determine if they have an adequate and quality sample. If so,
direct typing using the A-B-O system is done. The blood type
can be classified as A, B, AB or O based on the specific
agglutinogen present in the red blood cells.
Blood begins to dry after 3-5 minutes of exposure to air. As it
dries, it changes color towards brown and black. If the blood stain
has dried, indirect typing would have to be done. The most
common technique used is the absorption-elution test. It is done
by adding compatible antiserum antibodies to a sample, then
heating the sample to break the antibody-antigen bonds, then
adding known red cells from standard blood groups to see what
coagulates.
5. Can the sex, age, and race of the source of blood be
determined?
The sex of the blood source can be determined by observing
a distinctive drumstick-like structure called Barr body in white
blood cells. Their appearance in blood of unknown origin is a
basis for identifying it as from a female.
The color of dried blood changes in time from red to brown,
and the peroxidase test takes longer to develop with an old stain.
It is now possible to measure color-change scientifically.
Spectrophotometric analysis of bloodstains allows them to be
aged within the range of one day to three weeks.
Certain albeit controversial racial genetic markers involving
protein and enzyme tests help determine race. The ABO system
of typing blood including the Rh factor has certain proportions
within a population but this is not entirely helpful.
6.
Are there other tests that can be done on blood found in
a crime scene?
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.
DNA can be extracted from blood if white blood cells which
always contain a nucleus are present. The DNA extracted and
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CPU-Net MEDICAL ALERT | Jan - Feb 2005 | Volume 3, Issue 1 | Page 2
analyzed can then be matched with that of a suspect. This is the
most reliable test at present that could be used in identifying the
source of blood in a crime scene.
7. Can parentage be determined by blood types?
x
The rapid development of new genetic markers during the
past 40 years has greatly enhanced our ability to identify
particular people by testing their blood. As more polymorphic
markers are recognized and utilized, it will undoubtedly become
clear that no 2 related individuals are alike. Although blood typing
was once used as a tool in determining parentage, this system is
completely inconclusive. Even the most uncommon blood type is
shared with at least 10% of the population, meaning millions of
other men are just as likely to be the father. Elimination by blood
type is also inconclusive because it does not take natural mutation
into account. Application of DNA technology has now replaced
blood groups and serum markers in forensic studies.
8. Are there instances when the ABO blood grouping can
be compromised?
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Mobile Hotline: 0917-8900445
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x
x
x
Unfortunately, there are situations which can lead to
discrepancies in ABO blood typing. These are:
Clerical error: There should be a rigorous protocol in
specimen collection. This is not only important in cases of blood
transfusion but also in collecting forensic evidence. We can
emphasize enough that the chain of evidence not be
compromised at all from collection, transport of the evidence to
testing and submission of the results.
Technical factors
x
INFECTED RBCS. Infected red cells can be agglutinated by
normal human serum. These cells will test as AB when the
individual is actually group O, A or B. Thus, red cells should
be tested as soon as possible and stored properly as clotted
specimen at 4 C.
x
FIBRIN CLOTS. Small fibrin clots especially in long standing
specimens may appear as agglutination and read as another
blood group when tested.
x
MISCELLANEOUS ANTIBODIES. Antibodies to the testing
reagents such as dyes or preservatives may be present in the
blood sample that would cause false positive agglutination
reaction when testing for blood types.
x
LEVELS OF NATURALLY OCCURRING ANTIBODY. If a person’s
antibody production is too low as in the case of newborn
babies and the elderly, they may not produce enough anti-A
or anti-B levels that would result in accurate blood group
testing.
x
If blood stains are left for a long time, testing it will result in
blood group “O” even if this is not the original blood type.
Moreover, if there are two or more different blood types
admixed in a stain, e.g. A and O, only blood type A will be
identified and not the other blood types present.
CHILD PROTECTION UNIT NETWORK
x
Discrepancies due to disease processes
TRANSFUSION. If an individual has been transfused red cells
from a different but compatible blood group e.g. O Rh
negative cells, mixed field reactions may result.
BONE MARROW TRANSPLANT. In certain cancers, a person
may get a bone marrow transplant. This involves killing the
person’s own bone marrow with chemotherapy then
transfusing healthy bone marrow. If the blood group
transfused
differs from the recipient, a mixed field
reaction may be observed due to mixed reaction of the
person’s own residual red cells and that of the donor marrow.
LEUKEMIA AND MALIGNANCIES. The levels of A and B antigens
are decreased in leukemia, Hodgkin’s disease, and
lymphoma. There may be mixed field reaction with ABO
typing due to weakened agglutination.
ACQUIRED B PHENOTYPE. Scientists have realized that the red
cells can actually acquire an antigen of B type. This is caused
by certain bacteria such as Proteus and Clostridium, which
produce substances similar to A, B, and other blood type
substances, and thus may result in false grouping.
PARAPROTEINS. Myeloma and other diseases produce large
amounts of abnormal proteins that can cause false
agglutination reaction resulting in false blood typing.
9. Can blood not be typed?
The case of the Bombay phenotype. Rare individuals with
Bombay phenotype will test as Type O blood. When this blood
group was first encountered, it was found not to be of either group
A or B and so was thought to be of Group O. But on further test, it
did not match even for O Rh negative or O Rh positive because of
the absence of Antigen 'h'.
Individuals with Bombay phenotype blood groups can only be
transfused with blood from other Bombay phenotype individuals.
Given that this condition is very rare to begin with, any person
with this blood group, who needs an urgent blood transfusion,
would have a huge problem as it would be quite unlikely that any
blood bank would have any in stock.
References:
http://faculty.ncwc.edu/toconnor/425/425lect13.htm
http://www.policensw.com/info/forensic/forensic6b.html
http://en.wikipedia.org/wiki/Blood_type
http://www.bh.rmit.edu.au/mls/subjects/abo/resources/testing5.htm
Nathan D & Oski F, Hematology of infancy & childhood 4th ed, Saunders 1993
ANNOUNCEMENT
CPU-Net Workshop
“CHILD ABUSE (SHAKEN BABY SYNDROME) INVESTIGATION”
Lecturer/Facilitator: Mr. Craig Smith, Canadian Police
4 April 2005, 8am to 5pm
Traders Hotel Manila
RSVP: Not later than March 21
Experts on DNA & child rights issues available on-line to answer your questions.