Forensic Serology
Identification Using
Bodily Fluids
STEM
Forensic Serology
Serology – term used to
describe a broad range
of laboratory tests using
reactions of blood serum
and body fluid
Forensic Serology
The serology section of a forensic
laboratory deals with the following:
• blood typing
• characterization of unknown blood
• stain patterns for crime
reconstruction
• paternity testing
• DNA identification techniques
The Composition of Blood
Blood is a mixture of many
components:
•cells
•inorganic substances (salts)
•enzymes
•water
•proteins
The Composition of Blood
• 55 % of blood content is plasma – mostly
water and substances dissolved in it
• Most of the solid materials are cells
- red blood cells, RBCs (erythrocytes)
- white blood cells, WBCs (leukocytes)
Blood – Physical
Characteristics
• Adult ♂ contains 5-6L - Adult ♀ contains 4-5L
• Temp is about 100.4 F
– higher or lower than normal body T?
• 5 times as viscous as water
– more or less resistant to flow than water?
– what accounts for its viscosity?
• pH ranges from 7.35 – 7.45 (slightly alkaline)
• Color ranges from scarlet (oxygenated blood)
to a deep red (deoxygenated blood).
Three questions that must be answered by the
forensic investigator:
1) Is it blood?
Benzidine Test
Kastle-Meyer Test
Hemastix (o-tolidine, TMB)
Luminol Test
2) Is it human blood?
Precipitin Test
3) Can it be associated with an individual?
• Red blood cells contain
Luminol
hemoglobin (Hb) – for transporting
oxygen, which is made of iron
• Luminol reacts with iron and
becomes visible under UV light
Luminol
Blood Antigens
• On the surface of red blood cells are
chemical structures (proteins) called
antigens
• Antigens allow a living system to
recognize foreign substances
• Antigens also have characteristics and
can be used to identify individuals
• Human red blood cells have more than
15 different antigen types, but we’ll
focus on two
Blood Typing
Blood typing involves determination of the
antigens present on an individual’s RBCs
Blood Typing
The two most common blood typing
systems are the A-B-O and the Rh methods
type A blood – contain “A” antigen on RBCs
type B blood – contain “B” antigen on RBCs
type AB blood – contains A & B antigens
type O blood – contain no A or B antigens
Rh+ blood – contains Rh antigen
Rh- blood – no Rh antigen
Blood Typing
When blood
encounters free
oxygen (like in a
cut), the blood
clots, or
agglutinates
The clots can then be
removed by the host
system
Blood Typing
Human serum containing
specific antibodies can be
purchased
Separately mix a drop of
unknown blood sample
with drop of each antiserum
Reaction between blood
and anti-serum
No reaction between
blood and anti-serum
Blood Stain
Patterns
Dexter Blood Stain Pattern Video Clip
Catching Killers - Blood Stains 101 -Video Clip
Blood Stain Pattern
Analysis
Categories of Bloodstains:
•Passive (dripping)
•Transfer (smearing)
•Projected
Projected Bloodstains occur in shootings,
trauma from blunt weapons, hacking, or
slashing attacks.
Projected Bloodstain Analysis
Two Important Determinations:
a. direction of spatter
b. angle of impact with surface
sin  = (width drop / length drop)
Forensic Characterization of Saliva
Saliva is a mixture of many components:
•
99% water
•
Mucin (protein helps in swallowing)
•
Amylase (enzyme to digest carbos)
Cheek cells (good for DNA)
Adults produce 1.0-1.5 liters of saliva/day
and it is not uncommon at crime scenes
(especially involving bite marks).
Forensic Characterization of Saliva
• A simple test for saliva involves mixing
starch, iodine, and a sample of the
presumed saliva together.
• Starch and iodine are a deep blue color
when mixed together. The amylase
breaks down starch, however, and the
color fades
(takes about 15 mins @ 37 oC).