Forensic Serology Blood Most common blood types O

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 percent B Rh negative --- 2 percent AB Rh positive --- 3 percent AB Rh negative --- 1 percent O 43% Overall: A 42% B 12% AB 3%

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

Karl Landsteiner n n n 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

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

Forensic Scientists n n Until the early 1990’s, 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

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

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

Blood Components

Antigens n n n n 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 person’s blood type

D Antigen n n 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

Antibodies n n n 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

What would occur if… n We transfuse type A blood into a type B patient? n This would cause… It is only the antigen that will produce a response and bring on an attack