Every person's blood falls into one of the four international blood groups identified in 1900 by Dr Karl
Landsteiner. The ABO blood grouping system is a function of the red blood cells, and the presence in them
of a substance known as agglutination (becomes a compound). Absorption-elution technique is one of the
few techniques used for analysing visible blood stains on numerous surfaces using this system. Unlike other
techniques, this technique allows this blood type to be known narrowing the blood spatter down to the
correct victim. If the blood sample has the same blood type as the vicitm, then further analysis can be done
to prove 99.9% that it is the victim's blood. If not the correct blood type, suspects are able to be ruled out
acordingly.This technique begins with the antiserum being placed on the blood stained material, allowing
sufficent time for the antibodies to combine with their specific antigens. Next, the unreacted serum is removed
by being washed off the blood stained material. Once an antibody combines with an antigen, it is possible to
break the complex apart by a process known as elution. To do this, the stained material must be heated
at 56 degrees Celcius. This allows the antibody-antigen bond to break, freeing both. When the eluted
antibodies are combined with known red blood cells so that the presence or absence of a compound can be
observed, they can be identified.
Bloodstain Test with:
Anti A Anti B Antigen Present Blood Type
+ + on Stain
A cells B cells
+ - A A
- + B B
+ + Both A & B AB
- - Neither A or B O
