Indirect typing would have to be done on severely dried stains, and the most common technique is the absorption-elution test . It is done by adding compatible antiserum antibodies to a sample, then heating the sample to break the antibody-antigen bonds, then adding known red cells from standard blood groups to see what coagulates. To answer Question 5, forensic scientists use various color and nitrate tests, as well as heredity principles to estimate things like age, sex, and race. In fact, the saliva and semen in such individuals have higher concentrations of A and B antigens than their blood. The forensic serologist often will want to analyze the stains of other body fluids.
Wet blood has more value than dried blood because more tests can be run.
For example, alcohol and drug content can be determined from wet blood only. Blood begins to dry after 3-5 minutes of exposure to air. As it dries, it changes color towards brown and black. Blood at the crime scene can be in the form of pools, drops, smears, or crusts . Pools of blood obviously have more evidentiary value in obtaining a wet sample.