Precipitin Test - OldForensics 2012-2013

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Precipitin Test
BY: KHIZRA YOUNIS
BRITTANY ALDARONDO
ALEJANDRO REYES
KEVIN MAC
Precipitin Test: How it is used
 The Precipitin test is used to help distinguish human
blood from a possible animal blood.
 Every creature creates protein and if another type of
protein is introduced in the system then the
creature’s body will not accept the proteins.
 The body will create antibodies for the foreign
proteins, investors take these antibodies out.
Precipitin Test: How it is used
 The serum taken will have the antibodies that react
to human antigen when human blood is added to the
serum.
 When the human blood is added to that serum then
it will precipitate if the blood is actually human.
Diagram
Visual of the Precipitin Test
Strengths
 The precipitin test is sensitive and will work on small
traces of blood.
 It determines whether the blood is from a human or
animal.
 It is easy to tell if it originated from a human from
the results.
 It takes about 24-48 hours
Weaknesses
 The precipitin requires antisera which is found in
rabbits.
 Humans have different size veins meaning that it can
be difficult drawing blood.
 The conditions that the test undergo are precise from
the temperature of the reaction and the timing.
 There has to be an optimal concentration of both
antigen and antibody.
Cases
 On Saturday morning, Mr. Lee went to go drop off his dog
at his pet day care. But something didn't feel right when he
entered. All the dogs were barking and seemed to be
irritated, which was very unusual.
 There was a new person at the front desk, and when Mr.
Lee asked for the regular receptionist, the man replied in an
agitated voice. Mr. Lee asked to use the bathroom and as he
was walking down the hallway, he saw bloodstains on one
side of the wall.
Cases (continued)
 He went back home immediately and called the police
and told them what he saw. The police came to
investigate and there they found traces of blood.
 Unable to determine whose blood it was, they took the
Precipitin test and realized it was human blood, not
animal.
 Originally, they had thought that a dog might have been
killed there. However, it turned out that the receptionist
had gotten into an argument with her boss and he had a
very short temper.
Review Questions
1.
What animal is mostly used in the precipitin test?
2.
What is the main purpose of the Precipitin test?
3.
What did Mr. Lee see in the hallway that made him call
the police?
4.
Will the Precipitin test work on small traces of blood?
5.
Is this test sensitive?
Cited Sources
 http://www.siracd.com/life/life_case2.shtml
 http://www.fmap.archives.gla.ac.uk/Case%20Files/Bloodtest/Bloodtest.htm
 http://meaganpickles.tripod.com/forensicbiology101/id8.html
 http://www.forensicsciencecentral.co.uk/biology.shtml
 http://www.slideshare.net/rubina1000/precipitin-protocol
 http://classes.midlandstech.edu/carterp/Courses/bio225/chap18/figure_18_0
3_labeled.jpg
 http://classes.midlandstech.com/carterp/Courses/bio225/chap18/1803_Precipitin_1.jpg
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