1. Bloodstains and Blood splatters
Serology
Bloodstains and Blood splatters

2. Characterization of Bloodstains
When examining dried blood, the criminologist must answer the following questions:
Is it blood?
From what species did the blood originate?
If the blood is of human origin, how closely can it be associated to a particular individual?

3. Is it Blood?
The determination of blood is made by using the Kastle-Meyers color test. The Kastle-Meyers test is a color test that utilized phenolphthalein.
The Kastle-Meyers test is based on the observation that blood hemoglobin possesses Peroxidase-like activity.

4. Is it Blood?
Peroxidases are enzymes that accelerate the oxidation of peroxides.
When a bloodstain, phenolphthalein reagent and hydrogen peroxide are mixed together, the blood’s hemoglobin will cause the formation of a deep pink color.

5. Kastle-Meyers Test

6. Is it Blood?
Phenolphthalein + Bloodstain + Hydrogen peroxide = pink color

7. Is it Blood?
A Hemastix strip, can also be used to test for blood. The strip is moistened with distilled water and placed in contact with suspected blood. If the strip turns green, blood is present.

8. Is it Blood?
Another blood identification test is the luminol test. The luminol is not a color change reaction, it is rather a light producing reaction.
Luminol reagent is spread over the suspect area and the emission of light is tested in a darkened area.

9. Is it Blood?
Luminol is extremely sensitive and can detect blood diluted up to 300,000 times.
Luminol does not interfere with DNA testing.

12. luminol + hydrogen peroxide  oxidised luminol + LIGHT
haemoglobin catalyst

14. Is it Human Blood?
Once the stain has been characterized as blood, the serologist needs to determine if it is of human origin.
The precipitin test is the standard test utilized in determining of blood is of human origin.

15. Precipitin test
The Precipitin tests are based on the fact that when animals (usually rabbits) are injected with human blood, antibodies are formed that react with the invading human blood to neutralize its presence.

16. Precipitin Test
The investigator can recover these antibodies by bleeding the animal and isolating the blood serum.
This serum will contain antibodies that specifically react with human antigens.
The serum is known as human antiserum.

17. Precipitin Test
Utilizing this same method, there are antiserums for dogs, cats and deer.

18. Precipitin Test Techniques for utilizing antiserum:
One is to layer an extract of the bloodstain on top of the human antiserum in a capillary tube.
Human blood will react by forming a cloudy ring or band where the two liquids meet.

20. Precipitin Test In Other words: Add human blood to rabbit
Rabbit produces antibodies against human blood
Bleed rabbit and separate serum (serum contains Human anti-bodies)
Add Human anti-bodies to blood at crime scene
If it precipitates (or clots) it is positive for human blood.

21. Precipitin tests
The precipitin test is very sensitive and can give a positive test for dried blood that is or more years old.
There have been positive precipitin tests of tissue from mummies that are four to five thousand years old.
Blood that has been washed and diluted can still give a positive precipitin test.

22. Gel Diffusion
Gel diffusion- is when antibodies and antigens are placed on an agar plate, they will diffuse or move toward one another
In the electrophoretic
method, an electrical
potential is added to the
gel.

23. Who does the blood belong to?
Once the blood has been determined to be human blood, an effort is made to narrow down the possibilities of suspects or victims.

24. Who does the blood belong to?
There are several factors that can be tested in blood to narrow down it’s origin.
A-B-O blood groups
Rh factor (positive or negative blood type i.e. A+ or A-)
Enzymes (especially PGM: phosphoglucomutase)

27. Who does the blood belong to?
The more factors a forensic serologists can find in a blood stain, the smaller the frequency of occurrence in a population.
In other words the more characteristics blood has, the more the a criminologist can narrow down possible suspects.