Forensic Science Serology – Blood Type Analysis

Serology - Blood Type Analysis Blood is perhaps most valuable evidence in forensics –its presence links suspect and victim to one another and crime scene

Blood Blood = red fluid composed of: red cells white cells platelets plasma Each person’s blood has certain inherited characteristics that distinguish it from other people’s blood. In early 1900s, Dr. Carl Landsteiner found four major blood groups (A, B, AB, and O) based on the reactions of donor red blood cells with recipient serum

Blood Inherited genes determine which proteins are produced in individual’s body ABO blood type determined by presence or absence of specific proteins (antigens) on individual’s red blood cells In ABO blood typing, blood proteins (antigens) are called A and B proteins (or A and B antigens)

Blood Presence or absence of the A and B antigens on the RBC determines individual’s blood type If contain protein A and lack protein B  have type A blood Have protein B and lack protein A  have type B blood Both proteins  AB blood Neither protein  type O blood

Genetics Example of multiple alleles – I A, I B, i Demonstrates simple dominance and codominance If I A i  blood type A If I B i  blood type B If I A I B  blood type AB (example of codominance)

PhenotypeGenotypeProtein on RBC (antigen) Antibodies in blood plasma (serum antibody) Type AI A I A or I A iA b anti-B sera Type BI B I B or I B iB a anti-A sera Type ABIAIBIAIB A and B --- Type Oii--- a and b anti-A and anti-B sera

Blood Antibodies, found within plasma, distinguish particular antigens on RBCs from others If foreign antigens are found, RBC either experiences –Bursting OR –Agglutination Usually it is necessary for exposure to an antigen to occur before antibodies are produced; however, in this case the antibodies are already present before any transfusion is attempted.

Blood Agglutination: –the antibodies bind the antigens from different red cells Figure shows what you have to look for in ABO blood test result Agglutinated blood or clumps indicate the presence of various blood types

The ABO Blood Typing Based upon clumping phenomena of bloods of mixed types Can isolate blood sera antibodies and use as blood typing sera Antibodies-b (Anti-A sera) would clump RBC containing A antigens

The ABO Blood Typing If attempt to transfuse type A blood into a type B recipient, the anti-A in the recipient’s blood will cause the A cells to agglutinate. The agglutinated cells will become trapped in capillaries –After several days, they will rupture and release breakdown products –These breakdown products may clog vital organs such as the kidneys –In extreme cases, the kidneys will fail and death will result

The ABO Blood Groups Safe transfusions can only occur when the antigenic properties of donor blood are compatible with the recipient’s antibodies. Conditions are safe when both donor and recipient belong to the same ABO blood group Type AB blood can receive blood from both type A and type B due to the presence of both a antigens and B antigens (universal recipient) Type O can give blood to all three types due to absence of antigens (universal donor) –usually only done in emergency situations

Blood Typing The commercial availability of anti-A and anti-B sera (blood sera containing antibodies against the A and B antigens respectively) allows the matching of donor and recipient, an important requirement of the modern blood banking system.

Blood Typing Results anti-A sera + bloodanti-B sera + blood Type AClumpsno clumps Type Bno clumpsClumps Type ABClumps Type Ono clumps To determine blood type, analyze results from blood typing test.

Other Blood Typing Systems Rh Factor

Rh Blood Group Has several antigen factors on surface of RBC If any of antigens are present, will result in clumping –Individual is identified as Rh positive (Rh + ) If RBC lack Rh antigens, no clumpng will occur –Individual identified as Rh negative (Rh - )

Rh Blood Group Rh factors are inherited Genetically, simple dominant/recessive situation –Rh + is dominant Antibodies for Rh (anti-Rh) don’t appear spontaneously but form due to exposure

Rh Blood Group If Rh-negative person receives transfusion of Rh-positive blood, recipient produces anti-Rh antibodies Generally, no serious consequences occur after initial transfusion If 2 nd Rh-positive transfusion is received, RBC likely to clump due to sensitivity to Rh-positive blood (has antibodies to Rh- positive)

Rh Blood and Pregnancy If Rh-negative woman is pregnant with Rh- positive fetus for the first time and their blood mixes during birth or miscarriage, mom can can produce antibodies to Rh- positive