Forensic Serology

Karl Landsteiner First person to recognize that all human blood is not the same Blood is distinguishable by its’ group or type Now called the A-B-O System Important because using the wrong blood cause instant death for those receiving transfusions Today there are more than 100 different blood factors known

Blood as Identification In theory, no two individuals, except for identical twins, could have the same combination of all individual blood factors (not just blood types) Blood factors are controlled genetically and have the potential of being a distinctive feature for personal identification Important in serious crimes where blood is found at a crime scene—homicides, assaults, and rape.

Blood as Evidence Blood typing not so useful anymore because of DNA technology Scientists can now characterize biological evidence by selecting regions of our DNA

The Nature of Blood Blood: complex mixture of cells, enzymes, proteins, and inorganic substances Plasma: the fluid portion of blood Mostly water 55% of blood content The other 45% is made of solid particles

The Nature of Blood Erythrocytes: red blood cells; found in plasma Leukocytes: white blood cells; found in plasma Platelets: clotting factor; found in plasma Serum: the liquid that separates from the blood when a clot is formed

Important Parts for Forensic Science Red Blood Cells—because of their importance in blood typing Serum—because of its’ importance in carrying antibodies

Red Blood Cells and Blood Types Protein resides on the Red Blood Cell called antigens Antigens give blood-type characteristics to the Red Blood Cells ABO and Rh systems are the most important blood types

Antigens and Blood Types Type A Blood has Antigen A on the surface of the Red Blood Cell Type B Blood has Antigen B on the surface of the Red Blood Cell Type AB Blood has both Antigen A and Antigen B on the surface of the Red Blood Cell Type O Blood has neither Antigen A nor Antigen B on the surface of the Red Blood Cell

Distribution of Blood Types in US Type O Blood is the most prevalent with 43% Type A Blood is the next most common with 42% Type B Blood is less common with 12% Type AB Blood is the most rare type with 3%

Rh Factor or D Antigen Blood that contains the D Antigen is referred to as Rh + Blood that does not contain the D Antigen is referred to as Rh -

A, B, D—that determines a person’s blood type. In routine blood typing, it is the presence or absence of the three antigens— A, B, D—that determines a person’s blood type.

Fundamental Principle of Blood Typing Serum contains proteins known as antibodies For every antigen, there is a specific antibody that reacts against it. Anti-A reacts against antigen B Anti-B reacts against antigen A When antibodies react against its’ specific antigen, agglutination or clumping of RBCs occur.

Blood Type Antigens on RBCs Antibodies in Serum Antigen A Anti-B B Antigen B Anti-A AB Antigen A and Antigen B Neither Anti-A nor Anti-B O Neither Antigen A nor Antigen B Both Anti-A and Anti-B

What is Serology? The term serology refers to a broad scope of laboratory tests that use specific antigen and serum antibody reactions. Blood typing falls into this category.

Forensic Characterization of Blood Stains Important Questions: Is it blood? From what species did the blood originate? If the blood is human, how closely can it be associated with a particular individual?

Preliminary Determination of Blood Sample tested with phenolphthalein Turns deep pink color Positive for blood Also known as the Kastle-Meyer Test Use of Hemastix When moistened with distilled water and placed in contact with stain, a bright green color indicates blood.

Preliminary Determination of Blood Luminol Test Produces light if blood is present in a darkened area Extremely sensitive: can detect stains diluted up to 300X Will not interfere with any subsequent DNA testing

Is it human blood? Precipitin Test: Human blood is inserted into animal (rabbit) Rabbits produce antibodies to react against the human blood Blood is drawn from rabbit that contains the human antibodiesproduces human antiserum Unknown blood sample, if human, will react with the human antiserum from the rabbit by forming a precipitate

Is it human blood? Gel Diffusion and Electrophoresis Antibodies and antigens will move toward each other on an agar gel plate or in an electrophoresis chamber Forms a precipitate where the human antibodies and antigens meet No precipitate? Unknown sample is not human blood

Effectiveness of Tests for Human Blood Precipitin Test: Very sensitive and requires only a very small amount of blood Works on very old samples Even in washed items blood may be detected