Forensic Serology

1
Forensic Serology

• Blood

• Most common blood types
• O Rh positive ---   39 percent O Rh negative
  ---   9 percent A Rh positive ---   31 percent
• A Rh negative ---   6 percent B Rh positive
  ---    9 percentB Rh negative ---   2 percent
  AB Rh positive ---  3 percent AB Rh negative
  --- 1 percent
• Overall
• O 43 A 42 B 12 AB 3

2
Blood

• For years, doctors tried to transfuse blood from
  one patient to another
• Their efforts ended in the patients body
  accepting the transfusion, or rejecting it
• If rejected, the blood would coagulate,
  agglutinate, or clot, and the patient would die

3
Karl Landsteiner

• Discovered blood typing in 1901
• Earned him the Nobel Prize 29 years later
• He recognized that all human blood was not the
  same
• Out of his work came the classification system we
  call the A-B-O system
• Now docs had the key for properly matching the
  blood of a donor to the recipient
• You cannot mix one blood type with another, if so
  there are disastrous consequences

4
Other Discoveries

• 1937 the Rh Factor was discovered (positive or
  negative blood)
• Shortly after, numerous blood factors or groups
  were discovered
• More than 100 different blood factors have been
  identified so far

5
Forensic Scientists

• Until the early 1990s, they would focus on blood
  factors for linking blood to an individual
• They would do this because, in theory, no two
  people, unless identical twins, could have the
  same combination of blood factors
• They are controlled genetically and are very
  distinctive in personal identification
• Blood found at crime scenes can be identified by
  the factors and can thus link a suspect to the
  crime

6
DNA

• Scientists no longer look for these factors, but
  characterize evidence by DNA, which carries the
  bodys genetic info
• Dried blood and other biological evidence can be
  tested by this DNA technology
• Where can you find DNA in blood?

7
Nature of Blood

• Blood is a mixture of
• Plasma fluid portion of unclotted blood, made
  mostly of water, and accounts for 55 of the
  blood content
• Suspended in the plasma are solids consisting of
  several cells- RBCs (erythrocytes), WBCs
  (leukocytes), and platelets. This accounts for
  45 of blood content
• Serum is the liquid that separates from blood
  when a clot is formed

8
Blood Components
9
Antigens

• On the surface of each RBC, chemical structures
  called antigens, are found
• The most important antigen systems are the
  A-B-O and Rh systems
• If a person has A blood, then they have A
  antigens
• B blood has B antigens
• AB blood has both A and B antigens
• O has no antigens
• The presence of A and B antigens determines a
  persons blood type

10
D Antigen

• Rh factor, or D antigen
• If a person has the D antigen, they are Rh
  positive
• If they lack it, then they are Rh negative
• The presence or absence of three antigens-A, B,
  and D- must be determined in testing
  compatibility of the donor and recipient

11
Antibodies

• Serum contains proteins called antibodies, which
  destroy a specific antigen
• An antibody reacts only with its specific antigen
  and no other
• Type A blood has A antigens, anti-B antibodies
• Type B blood has B antigens, anti-A antibodies
• Type AB has A and B antigens, no antibodies
• Type O blood has no antigens, anti-A and anti-B
  antibodies

12
What would occur if
It is only the antigen that will produce a
response and bring on an attack

• We transfuse type A blood into a type B patient?
• This would cause