Forensic Serology

Forensic Serology

Forensic serology is the application of the study of blood, semen, saliva and other body fluids, to legal matters. The field generally is comprised of the detection of enzymes and antigens, as in the identification of seminal stains or blood typing (ABO and secretor status) and DNA typing (by PCR or RFLP analysis).

The serology section of a forensic laboratory may deal with any or all of the following:
* blood typing
* characterization of unknown blood
* blood spatter analysis for crime reconstruction
* paternity testing
* semen identification in rape cases
* DNA techniques used for identification

The Composition of Blood
Blood is a mixture of many components:
cells inorganic substances (salts)
enzymes water
proteins
Forensic Characterization of Bloodstains
Three questions that must be answered by the forensic investigator:
1) Is it blood? Use presumptive tests:
Kastle-Meyer
Leuchomalachite Green
Luminol
2) Is it human blood?
Precipitin Test
3) Can it be associated with an individual?
DNA

Is It Blood? Presumptive Tests for Blood

Luminol
* Red blood cells contain hemoglobin (Hb) – the protein responsible for transporting oxygen
* Each Hb contains four iron (Fe) containing hemes
False Positives
Precipitin Test Procedure
* animal (usually a rat or rabbit) is injected with human blood
* animal’s blood forms antibodies
* antibodies are harvested from animal’s blood serum (“antiserum”)
* in a test tube, an extract from the suspected bloodstain is addedto the antiserum
* if a precipitate forms where the two meet, it is human blood

Confirmatory Tests
Blood Typing: Antigens
Blood Typing Example
A sample of unknown blood is mixed with three anti-sera samples:
Tube 1 (Anti-A): No reaction
Tube 2 (Anti B): No reaction
Tube 3 (Anti Rh): Cloudy reaction
Characteristics of Blood
CLASS
Species
Type
Disease
Rh factor
INDIVIDUAL
DNA
Bloodstain Analysis
Categories of Bloodstains:
Passive (dripping)
Transfer (smearing)
Projected
Projected Bloodstain Analysis
Two Important Determinations:
a. direction of spatter
b. angle of impact with surface
Forensic Characterization of Semen
Many crimes involve sexual assault. Forensic Investigators may need to search for semen stains at a crime scene. Bedding, clothing, carpets, cushions, vehicle seats, etc.

Seminal Fluid contains:
* water, spermatozoa, enzymes, inorganic salts
Presumptive Tests

Confirmatory Test Required
Microscopic examination of sperm
False Positives
Forensic Characterization of Saliva

Forensic Serology.ppt