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Serology
Serology
• Blood is the bodily substance most
commonly found at the scene of a crime or
on a person, clothing, or a weapon
potentially associated with a crime.
• Discussion of serology into three sections:
the principles of forensic serology, the
conventional analyses of blood & other
body fluids, and DNA testing.
Serology Principles
• The science that studies the properties &
effects of serums such as analysis of
blood traces is called serology.
• Types of biological evidence: notably
blood, semen, saliva, perspiration, and
fecal matter.
• Tests to identify blood have been known
since at least 1875.
Serology Principles
• It could not be applied to dried blood nor
could it distinguish between human blood
and that of other mammals.
• Most important test of the time was the
guaiacum (tree resin) test. Suspected
blood placed in water, added guaiacum
then hydrogen peroxide. Blue color =
blood. Could be used with very tiny amt. of
blood - ? Human or other animal though
Serology Principles
• Breakthrough in identifying human blood
came as a development of experiments of
Paul Ehrlich that led to establishment of
new scientific discipline: immunology.
• An “immune” serum against certain toxic
substances could be obtained by injecting
substance into an animal in small doses.
• An antiserum (a serum with antibodies)
could subsequently be taken from animal.
Serology Principles
• If toxin & antiserum were together injected
into another healthy animal, toxin would
produce no ill effects. (vaccine)
• Karl Landsteiner showed serum of certain
persons would agglutinate (clump) red
blood cells of certain other persons
because red blood cells contain antigens
or blood-group factors & the blood serum
contains antibodies.
Serology Principles
• Two antigens are A & B and antibodies
are anti-A and anti-B.
• Persons with antigen A contain anti-B
antibodies: Type A blood. Persons with
antigen B contain anti-A antibodies: Type
B blood.
• Persons with both antigens, neither
antibody: Type AB blood. No antigens,
both antibodies; Type O blood.
Serology Principles
• 1915: Dr. Leon Lattes, Asst. Researcher at
Institute of Forensic Medicine at University
of Turin, Italy, developed a procedure to
apply ABO testing to bloodstains on cloth
& other materials.
• He used saline solution to dissolve dried
blood from cloth.
Serology Principles
• 1910, scientists concluded blood groups
could be utilized as evidence in paternity
suits & in other criminal investigations.
• 1985, Alec Jeffreys & colleagues
discovered that portions of DNA structure
of certain genes are unique to each
individual. Termed the process used to
isolate & read these genetic markers as
“DNA fingerprinting”.
Serology Principles
• It is now known that ABO antigens are not
limited to red blood cells.
• Some 80% or more people have their
blood-type antigens in most of their body
fluids including saliva and perspiration.
Such individuals are known as secretors.
Serology Conventional Analysis
• Excluding hormones, more than 160
antigens, 150 serum proteins & 250
cellular enzymes are recognized.
• Although some of the old tests for blood
have been greatly improved & some
sophisticated new methods have been
developed, the standard procedures still
largely apply.
Serology Conventional Analysis
• These include preliminary tests to identify
blood (or semen, etc.), followed by tests
for species, blood grouping, & other
factors.
• The goal is to reach or at least approach
as closely as possible the individualization
of a sample of blood or other biological
evidence.
Serology Conventional Analysis
Preliminary Tests
• First identify a suspect substance as blood
before proceeding to more complex tests.
• Most tests are for blood enzyme called
peroxidase. Some substances can give
similar “false positive” reactions such as
horseradish. Therefore, preliminary blood
tests are called presumptive tests used for
screening. If positive, other tests required
to identify the substance as blood.
Serology Conventional Analysis
Preliminary Tests
• Benzidine test was standard preliminary
blood indicator but is highly carcinogenic &
no longer used.
• Phenolphthalein is becoming increasingly
used as blood indicator & called KastleMeyer color test; very sensitive test.
• It is mixed with hydrogen peroxide.
Positive reaction gives a deep pink color.
Serology Conventional Analysis
Preliminary Tests
• Luminol test: develop invisible traces of
blood, especially older dried blood stains.
• Even smear marks caused by wiping or
mopping in attempts to remove blood
stains can be “visualized” by using luminol.
• Caution: experience needed; glowing is
not always blood; actual bloodstains
produce areas of luminescence.
Serology Conventional Analysis
Preliminary Tests
• Stain is preliminarily identified as blood &
must be confirmed & determined to be
human or animal origin. Precipitin test
identifies proteins in blood based on fact
animals (typically rabbits) produce antibodies as result of injection of human
blood. Resulting anti-serum/anti-human
serum reacts positively to human blood
forming a white cloudy precipitate.
Serology Conventional Analysis
Preliminary Tests
• Appropriate controls are tested at same
time as suspected blood to ensure antiserum is both accurate & specific.
• Once blood is determined to be human, it
is then classified as to blood grouping.
• Most common groups are A & O which
constitute about 39% & 43% respectively
of general population.
Serology Conventional Analysis
• Additionally discovered blood factors
permit increased blood characterization
(Rh & MN). Some of other blood parts
(plasma proteins & enzymes) may be
identified by electrophoresis.
• Using a number of factors together greatly
narrows the frequency that a given blood
sample can be expected to occur in a
population.
Serology Conventional Analysis
• Semen may be identified microscopically
by presence of sperm. They are very
brittle when dry & disintegrate easily with
handling or washing.
• Preferred method of locating & identifying
simultaneously a seminal stain is by the
acid phosphatase color test (enzyme
secreted by prostate gland). Purple =
positive reaction meaning sperm present.
Serology Conventional Analysis
• Although other substances, notably fungi,
contraceptive creams & vaginal
secretions, also react positively to the acid
phosphatase test. Difference is that none
of the other substances usually react as
fast as seminal fluid (under 30 seconds).
• Other methods are used to confirm
identification such as testing for p30
protein.
Serology Conventional Analysis
• Other biological evidence includes urine,
perspiration, saliva, feces, vomitus &
vaginal secretions. Except for vaginal
secretions, these types of evidence are
rarely encountered.
• Paternity determination is another type of
conventional serological analysis although
not usually relevant to a criminal
investigation.
Serology Conventional Analysis
• We use blood-grouping systems with
suspected parents & offspring using the
human leukocyte antigen (HLA) test rather
than ABO system. Leukocyte = white
blood cell.
• Currently, DNA testing can increase the
probability of paternity to more than 99%.
Serology DNA Testing
• The 1911 discovery of deoxyribonucleic
acid (DNA) – the carrier of genetic
information – caused scarcely a ripple in
medical jurisprudence.
• When Alec Jeffreys discovered the
individuality of DNA genes with DNA
fingerprinting, it revolutionized forensic
serology.
Serology DNA Testing
• On November 21, 1986, legal & forensic
history was made when the kitchen porter
became the 1st accused murderer to be
cleared as a result of DNA fingerprinting.
• Like fingerprints, DNA can be used to
make a positive identification. Unlike
prints, DNA is inherited, so a small
segment of the DNA chain will be identical
in all blood relations.
Serology DNA Testing
• One advantage of DNA is that it is found
everywhere white blood cells are found.
• DNA structure – twisted ladder or spiral
staircase called double helix made up of
subunits called nucleotides consisting of a
sugar (deoxyribose), a phosphate, & 4
kinds of nitrogenous bases: adenine,
guanine, cytosine, thymine. A pairs with T,
C pairs with G
Serology DNA Testing
• The microscopic DNA strands are folded
into structures called chromosomes &
exist in all cells with a nucleus (except red
blood cells = lack nuclei).
• In addition to body fluids, DNA is present
in tissues, hair roots, bone marrow & tooth
pulp.
Serology DNA Testing
• For forensic purposes, there are two basic
DNA procedures in use: restriction
fragment length polymorphism (RFLP) &
polymerase chain reaction (PCR).
• Mitochondrial DNA will be discussed later.
• RFLP is used more often in forensic work.
Serology DNA Testing
• Its disadvantages are that it requires a
larger sample than PCR, is timeconsuming & labor intensive, & utilizes
radioactive reagents that require special
lab procedures.
• Its great advantage is that it can
individualize a specimen to a narrow
portion of the population – possibly one
person in billions.
Serology DNA Testing
• In contrast, PCR is faster & simpler to use
& may be applied to exceedingly tiny
samples.
• The technique is based on the way DNA
strands reproduce themselves in a cell.
• With PCR, an enzyme known as DNA
polymerase can be directed to duplicate a
strand of DNA several million times.
Serology DNA Testing
• Unfortunately, the results of PCR are less
dramatic than RFLP, being discriminatory
on the order of one individual in thousands
like the potential billions with RFLP.
• Another important investigative capability
utilizing DNA evidence is now under
development by the FBI laboratory.
Serology DNA Testing
• It is a national computerized network that
compiles databases of various states that
require sex criminals & sometimes other
violent offenders to provide blood for DNA
testing & recording. It’s called CODIS =
Combined DNA Index System.
• CODIS linked a 1991 Miami rape case
with a man who had been convicted of
sexual assault in Orlando in 1993.
Serology DNA Testing
• Before CODIS, the police had not even
identified a suspect in the case.
• Courts have sometimes challenged DNA
evidence on specific grounds such as
private labs failure to comply with suitable
standards & appropriate controls.
Serology DNA Testing
• However, properly applied DNA testing is
widely accepted as admissible under the
standards set by Frye or Daubert.
• Per Attorney General Janet Reno’s
comment: “Our system of criminal justice
is best described as a search for the truth.
Increasingly, the forensic use of DNA
technology is an important ally in that
search.”
Serology Case Study
The O.J. Simpson Trial
• Read Case Study & Watch A & E Video
“Why O.J. Won”. Do video quiz for grade.
• Listen to DNA evidence presented
disregarding comments by defense,
prosecution, evidence omitted by judge
that jurors could not hear or see.
• You determine – guilty or not guilty.
• Remember… DNA doesn’t lie!!!