serology Flashcards
serology
examination of blood, saliva, semen, and urine
what decades was forensic serology most important in lab procedures?
1950s-80s
blood
a complex mixture of cells, enzymes, proteins, and inorganic substances
plasma is what in blood
fluid portion
what percentage of blood is plasma
55%
what does plasma contain
Nutrients, hormones, clotting factors
Antibodies
what percentage of blood is cells
45%
what cells are in blood
red blood cells, white blood cells, platelets
ratio of cells in blood
For every 600 red blood cells, you have 40 platelets and 1 white blood cell
4 main blood groups
a
b
ab
o
who discovered the 4 types of blood
Karl landsteiner
rh factor
determines if blood type is positive or negative
who discovered the rh factor
Landsteiner and Weiner
antigen
proteins on a red blood cell
what are antigens responsible for
blood type characteristics
if you have the A antigen, what blood type do you have
type A
what does the D antigen determine
rh factor
what percentage of white people are Rh postive
85
what percentage of black Americans are Rh positive
94
what percentage of Asians are Rh positive
99
what is plasma mostly made of
water
role of antibodies in plasma
fight infection
If you have the Rh factor, your blood type is
positive
If you don’t have the Rh factor, your blood type is
negative
why is it useful to know the antigen of blood
used in routine blood banking for compatibility
what are antibodies produced by
immune system
what do antibodies react with
certain antigen
anti-A antigen is specific for ONLY
the A antigen
antiserum
serum containing the antibody
agglutination
the clumping of RBC’s by the action of an antibody
what 3 questions must be answered when examining dried blood
Is it blood?
From what species did it originate?
If human, how closely can it be associated with a particular individual?
how is the determination of blood best made
preliminary color test that detects hemoglobin
what does the Kastle-Meyer Color Test test for? what happens if its positive for that?
tests for hemoglobin
if hemoglobin is detected, it turns deep pink
is the Kastle-Meyer Color Test specific for blood?
no, also works for potatoes and horseradish
what is hemastix?
presumptive field test for blood
how does the hemastix test work?
dampen area with water, if it’s positive for blood, it will turn a blue-green color
luminol
produces light in a darkened area
what is luminol used for
to search out trace amounts of blood located at crime scenes
blue star test
similar to luminol but does not have to be used in a darkened area
how sensitive is the Blue star test?
extremely
capable of detecting bloodstains diluted to 1 in 100,000
Precipitin Test determines
if the blood is human origin
what does the Precipitin Test use antibodies from? how does it work
rabbits
rabbit injected with human blood causing a reaction to neutralize the foreign substance
created a human antiserum and a precipitin band if blood is of human origin
how does gel diffusion work
antibodies and antigens diffuse toward each other on an agar plate
precipitation line indicates a positive result
Immunoassay Techniques uses
antigen-antibody reactions in urine or semen
Immunoassay Techniques are able to detect
drugs in urine
Enzyme Multiplied Immunoassay Technique (EMIT) is able to detect
drugs in urine
are immunoassay techniques presumptive?
yes
Enzyme Multiplied Immunoassay Technique (EMIT) process
Add suspect’s urine antibodies that bind to drug class
Add chemically labeled version of drug
Competition between labeled and unlabeled drugs for antibody binding
No competition→ (+) drug screen
do you need to confirm Enzyme Multiplied Immunoassay Technique (EMIT)?
yes, usually spectrometry
Polyclonal antibodies recognizes
multiple sites on the same antigen
Polyclonal antibodies properties
quick and inexpensive to produce and able to be done on a live animal
vary between batches leading to specificity variation for an antigen site (epitope)
Monoclonal antibodies properties
designed to attach one and only one site on antigen
made from a single antibody producing B cell
able to produce large quantities of identical antibodies
forensically→ high specificity→ more accurate results for drugs and semen
what 2 things do you have to test for seminal stains?
presence of spermatozoa or of p30
p30
a protein unique to seminal plasma
Link seminal material to an individual by
DNA typing
acid phosphatase
an enzyme secreted by the prostate into seminal fluid
how to determine presence of acid phosphatase
Use a color test to determine presence
purple color is positive
forceful physical contact may transfer
blood, semen, saliva, hair, fibers
if a person is raped, they should get
a medical exam asap
what should happen/be collected during a post-rape medical exam
Physical evidence can be collected for 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
if a suspect is apprehended within 24 hours of a rape,
possible to detect the victim’s DNA on the male’s underwear or on a penile swab of the suspect
6 things a bloodstain can tell you
Direction from which blood originates
Angle drop struck the surface
location/position of the victim
Movement of the bleeding individual
Minimum number of blows
Approximate location of person delivering blows
satellite spatter
small drops of blood found around the main pool
satellite spatter happens as a result of
blood impacting a surface
do hard, nonporous surfaces have more/less spatter?
less
do rough surfaces have more/less spatter
more
higher the drop falls = more/less spatter?
more
Shape of the bloodstain indicates
if there was movement when it was deposited and if so, what direction the movement was in
angle of impact
the angle formed between the path of the blood drop and the surface it connects
what angle of impact will droplets from a stationary object have?
circular shape, no tails/spines
what angle of impact will droplets from a moving object have?
elongated shape when the strike a surface with tails and spines
pointed end of the blood stain (tails and spines) faces the direction of
travel
how to calculate angle of impact?
inverse Sin A= width of stain (mm)/length of stain (mm)
error rate of +/- 5 degrees
spatter pattern
bloodstain resulting from airborne blood drop
spatter pattern created when
external force is applied to liquid blood
3 types of spatter pattern
impact
forward
back
most common spatter pattern
impact
impact pattern results from
object striking liquid blood
forward pattern
projected outward, away from the source. Ex: exit wound
back pattern (blow back)
projected backward from the source and potentially deposited on the person or object that created the spatter. Ex: entrance wound
Area of Convergence
2D plane from which the drops originated
how is area of Convergence established
by drawing straight lines through the long axis of several different blood stains following the lines of their tails; intersection= area of convergence
area of origin
the area in 3D space from which the blood was projected
how is area of origin determined
angle of impact and area of convergence
what does area of origin show
the position of the victim or the suspect
9 types of spatter patterns
gunshot, castoff, projected, expirated, void, contact/transfer, flows, pools, drip trails
backspatter is dependent on
distance between firearm and victim, location of injury, and size of wound
drawback effect
backspatter that strikes shooter and enters gun muzzle; close range
Cast-Off Spatter happens when
a blood covered object flings blood in an arc onto a nearby surface
pull back of bloody weapon in between blows;
what direction do the tails point in cast-off spatter
direction the object was moving
what can cast-off spatter indicate
direction and which hand was used
minimum number of blows delivered from the upward and downward arc pattern
in cast off spatter, size of drops correlates to
type of object used
small/pointed object will create _ blood drops
linear
large/blunt objects will create _ blood drops
wider
projected patterns happen when
suffers an injury to a main artery or the heart
spurting due to the continual pumping of the heart
what do vertical arcs show in projected pattern
fluctuations in b.p.; decrease in b.p.leaves large deposits
what color are projected patterns? why
brighter red because of oxygenation
Expirated Patterns happen when
blood expelled from nose or mouth due to an internal injury
expirated Patterns produce
a fine spatter with presences of bubbles and a light color due to blood mixing with saliva
void patterns created when
an object blocks deposition of blood on a surface
void patterns properties
may be on a nearby object or person instead
-blank space can give clues to missing objects and body position of victim and/or assailant
contact/transfer stains
-bloody object touches one without blood
wipe patterns
contact and removal without any other movement; feathering
flows
drops or large amounts of blood moving due to gravity
pools
collection of blood in a level, undisturbed place
perimeter stain
edges will dry to the surface usually within 50 seconds of deposition
drip trails can show
movement of weapon, victim
drip trails are common in
stabbings
drip trails are
series of drops separate from other patterns
Documenting Bloodstain Pattern Evidence
-photograph and sketch overall pattern to show orientation to the scene
grid method
set up a grid of squares of known dimensions over the entire pattern and use string and stakes
perimeter ruler method
rectangular border or rulers around the pattern
2 types of documentation in blood stains
grid method
perimeter ruler method
