Download Testing for Blood Evidence

Testing for Presence of
Blood Evidence
Notes 3.3
Is it Blood?
► Hemastix
 Designed to test for the presence of blood in
the urine, but can have applications in forensic
investigation
 The test will turn green if the stain is in fact
blood
 Destructive test--blood that comes into contact
with the hemastix cannot be used to extract
DNA
Is it Blood?
► Kastle-Meyer
Test
 A nondestructive test, i.e., DNA can be
recovered from the blood treated with K-M
protocol. It works best on old blood stains.
 The hemoglobin in the stain will oxidize and
react with the phenolphthalein indicator. The
stain is mixed with phenolphthalein and then
hydrogen peroxide.
 The test will turn pink if the stain is blood
 The enzymes in some vegetables (tomato,
potato, cucumber, horseradish) can cause a
false positive
 Must be read within 30 seconds
Is it Blood?
► Luminol
 The hemoglobin in the stain will oxidize and
activate the chemoluminescent properties of the
Luminol.
 Luminol is an aerosol sprayed on the stain.
Results must be observed within seconds.
 The test will produce blue or green light if the
stain is in fact blood
 Nondestructive test, i.e., DNA can still be
recovered from the sample (but can’t do blood
typing)
 Luminal tests do not indicate the amount or
distribution of blood. (see page 249)
Is it Human Blood?
► Precipitin
Test (Ouchterlony double
immunodiffusion) (see page 339)
 Human blood antibodies can be created by
injecting animals with human blood. This is also
done with human blood types (ABO).
 The bloodstain is placed on top of antiserum
containing the antibodies
 The test will form a cloudy ring if the stain is
human blood
 Destructive test
Science Behind the Precipitin Test
Whose blood is it?
► Antiserum
Tests
 Human blood antibodies are created against
type A and type B antigens (from animal
immune systems)
 The bloodstain is mixed with a solution
containing the antibodies
 The RBCs will agglutinate (a positive test) if the
antigens are present
 Destructive test
Figure 8-5
Figure 8–1
Agglutination
► Antiserum
A will
agglutinate with blood
containing antigen A
► Why
does the image to
the right indicate Type
A and not Type AB?
Agglutination
Identify the Blood Type!
Person 1
AB
Person 2
B
Person 3
A
Person 4
O
Identify the Blood Type!
12 Testable Possible Results
Unlike RBCs, White blood cells
contain DNA