DETERMINATION OF BLOOD 12.3 NOTES –

OBJECTIVES List and describe forensics tests used to characterize a stain as blood

DETERMINATION – COLOR TEST Benzidine color test discontinued because of carcinogenic effect Currently uses phenolphthalein called the Kastle-Meyer Based on the peroxidase like activity of hemoglobin which produces a deep pink color when applied to blood Hemastix strips – turns green with blood

DETERMINATION – LIGHT TEST Luminol – produces light rather than color when viewed in dark area (luminescence) Luminol extremely sensitive Can be diluted 300,000 times Will not interfere with DNA testing

DETERMINATION CONT. Precipitin test – used to determine if blood is animal or human Animals produce human antiserum when injected with human antigens Gel diffusion – antibodies and antigen will diffuse toward one another in an agar gel place forming a precipitation line or by electrophoresis

DETERMINATION = HUMAN ORIGIN Further tests to determine identity Historically used ABO and polymorphic enzymes Currently uses DNA

PGM ENZYME Iso-enzyme (phosphoglucomutase) Separated by electrophoresis 3 isomer variations: PGM 1 (58%); PGM 2-1 (36%); PGM 2 (6 %) A combination of antigens, enzymes, and proteins are calculated by the product of distribution in the population (i.e.: 42% x 58% = 24%)

12.3 QUESTIONS 1.Name the most common color test for blood and describe how it identifies bloodstains. 2.Describe how luminal is used to detect bloodstains. 3.Name two reasons why color tests are superior to microcrystalline tests for identifying blood. 4.What is the standard test used to determine whether blood is of human or animal origin and what is the principle underlying test? 5.Which technique takes advantage of the fact that antibodies and antigens move toward one another on a plate coated with a medium made from a natural polymer called agar? 6.In what technique can antigens and antibodies be induced to move toward one another under the influence of an electrical field?