serology in forensic

1. Serology in Forensic
Laboratories
By: Karmel Al-Khaldi

2. Serology
● Serology:
The study of bodily fluids.
● Serology in forensic science:
Identification of body fluids such as:
Blood
Saliva
Urine
Semen
in forensic laboratories to answer questions of interest to
the legal system.

3. Serology in Forensic Science
● DNA analysis helps in direct individualization.
Why serology?

4. Serology vs. DNA Analysis
Serology Tests DNA Profiling
● Helps in identifying the source of DNA
(type of body fluid)
→ Determination of context of crime.
E.g. Semen might indicate rape.
● Does not identify DNA
source.
● Fast, efficient, and inexpensive.
→ saves time and efforts by excluding
unnecessary analyses. E.g. DNA
profiling of non-human blood samples.
● Slower and expensive
● Identify proteins specific for body fluids
→ Less specific: helps in identification
● Depends on nucleic bases in
DNA specific for each individual
→ More specific: helps in
individualization

5. The Major Body Fluids
Blood
Semen
Saliva
Urine
Sweat

6. The Major Body Fluids
Blood
Semen
Saliva
Urine
Sweat

7. Blood
● Blood: a tissue composed of several types of cells in a
matrix called plasma.
● Plasma: 90% water
10%: proteins (hemoglobin as one of the major constituents)
urea
amino acids
carbohydrates
organic acids
fats
steroid hormones
inorganic ions

8. Blood in Forensic Labs
● Blood can be a good source of
information for investigators in
many ways. Examples:
1. Identification/individualization:
determination of blood source.
→ Biological Analysis Section
2. Detection of drugs and toxins.
→ Toxicology and Drugs Section

9. Blood in Forensic Labs
● Identification of blood in forensic labs is performed by
answering the following questions:
1. Is it blood?
2. Is it human (determination of species origin)
3. In which blood group is it classified?

10. Blood in Forensic Labs
●Identification of blood in forensic labs is performed by
answering the following questions:
1. Is it blood?
2. Is it human (determination of species origin)
3. In which blood group is it classified?

11. Test for the Presence of Blood
→ Question: Is there blood in the questioned sample?
Reaction of a testing chemical with the hemoglobin present in blood.
→ Answer: Reaction occurs: Yes: +ve result: there is blood.
Reaction does not occur: No: -ve result: there is no blood.
Positive test results (i.e. presence of hemoglobin) are indicated by:
1. Change to a certain colored form.
2. Emission of light of a specific wavelength.

12. Test for the Presence of Blood
Benzidine test: used by the FLD in Jordan.
→ +ve results indicated by a green-blue color.
→ Gives +ve results for all iron-containing samples such as rust-
contaning samples.
(Benzidine is carcinogenic)

13. Large-scale Blood Tests
→ In cases where:
1. The blood pattern or distribution
is important.
2. The tested area is large and
intricate.
● The testing chemical is sprayed onto the surface then
emitted light is observed. E.g. on such chemicals:
1. Luminol 2. Fluorescein

14. Large-scale Blood Tests
1. Luminol → in presence of
hemoglobin gives blue-
white to yellow green
color (+ve result).
● Very sensitive to the
presence of hemoglobin
● The blood pattern is visible
for up to 30 min in dark.

15. Large-scale Blood Tests
2. Fluorescein → preparation
is similar to luminol:
preparation contains a
thickener.
● Why adding a thickener?
Makes fluorescein stay on the
surface better than
luminol → easy to use on
walls and vertical surfaces.

16. Large-scale Blood Tests
● Flourescene must be
illumionated at 450
nanometers via an
alternate light source
(ALS) to be seen.
(goggles are used for
safety purposes).

17. Tests for Human Blood
● In some forensic laboratories: after detecting the
presence of blood, DNA analysis is applied directly.
● In Jordan: the biology section in the FLD performs a
confirmatory test.

18. Species Origin
→ Is the blood in the sample of human origin or not?
● Detection techniques depend on antigen-antibody
reactions between:
- Human blood (antigen) → in the questioned sample
- Human antiserum (antibody) → the test reagent
(Antibodies against plasma proteins)

19. Species Origin
→ Answer:
Yes: +ve result: blood is of human
origin.
No: -ve result: blood is NOT of
human origin.

20. Blood Groups
● Blood groups are:
1. Genetically controlled
2. Invariant throughout a person’s life
→ Excellent for classification and possible inclusion or
exclusion for legal purposes.
→ ABO blood grouping system: best known.
→ Used by forensic laboratories to narrow down the
search group.

21. Blood Groups
● ABO blood grouping:
Use antibodies against
antigens on the
surface of red blood
cells.
● Results: as in the
next table.

22. Serology Tests
● Specificity (Specific tests): the ability of a test to
detect one specific substance.
● Sensitivity (Sensitive tests): The ability of a test
to detect (sense) very small amounts of a
substance(s).

23. Serology Tests
● 2 types of tests for serological analyses:
1. Presumptive tests: highly sensitive with less specificity for
a particular substance.
E.g. Benzidine can detect minute amounts of blood in samples
but gives +ve result for all iron containing samples such as
rust contaning samples.
→ False –ve: dangerous: lead to the exclusion of important
blood samples. Positive control is used to avoid false –ve
→ All +ve results (including false +ve) are taken and we
move to the next step (confirmatory test).

24. Serology Tests
2. Confirmatory tests: highly specific with less
sensitivity to a particular substance.
E.g. Test for determining species origin gives +ve results
only when human blood present but inefficient in
detecting very small amounts of human blood.