Blood evidence. The examination of blood is divided into two parts. biological (serology) physical (spatter)

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Marvin Preston
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1 Blood evidence

2 Blood evidence The examination of blood is divided into two parts biological (serology) physical (spatter)

3 What can blood evidence tell you? manner of blood loss position of victim and suspect animal or human male or female blood type medical condition identify of injured

4 is it blood?

5 Is it blood? There are several tests 1. Kastle Meyer hemoglobin + phenolphthalein + hydrogen peroxide = deep pink color it is a presumptive test so a positive result should be confirmed false positives can come from some vegetables but they are unlikely to be at a crime scene!

7 Is it blood tests Hemastik 3. Luminol positive test produces light very sensitive stains diluted up to 300,000 times false positives possible covers large areas will not interfere with DNA testing

9 Miscellaneous info as blood dries it changes from red to brown spectrophotometric analysis of blood stains looks at color differences and can pinpoint the age of the blood from 1 day to 3 weeks

10 Let s look at the Biology of blood plasma = liquid part; mainly water; 55% of the blood contains antibodies (proteins that are part of the immune response)

11 blood layers solid materials = blood cells and platelets red blood cells (RBC) have antigens on cell surface for recognition white blood cells (WBC) have a nucleus so important in DNA typing Platelets (blood clotting)

12 Collection and Preservation of Blood Evidence In order for blood evidence to be used, a reference sample MUST be collected (from the victim, from the suspect, etc.) vacutainer tubes are used for collection allows the blood to stay liquid and fresh; blood is then useful for tests (blood type, DNA, etc.) After collection the blood reference sample must be refrigerated

14 Collection Start with moist blood first Collect in clean, unused plastic containers Use sterile cotton squares or swab Store wet in plastic for no more than 2 hours Once in lab dry the sample

15 Collection If dry... If surface is small and absorbent, collect in paper container If surface is large and absorbent cut out stains and place in paper container If surface is non-absorbent, scrape blood into a paper container If surface is non-absorbent, moisten stain with distilled water and absorb onto a piece of cotton

16 Collection and Preservation Dried blood stains left on clothing may not be useful difficult to determine when the blood was left and under what circumstances

17 Is the blood human or not human?

18 Human or non-human? 1. Precipitin test Every animal produces antibodies that react with each other s blood What to do... Add antibodies for suspected animal to blood sample; if a precipitate appears then the antibody matches that blood

19 Human or non-human? 2. Gel Diffusion Similar to precipitin test The container is changed Allows you to test several blood sources at a time

20 Human or non-human? The precipitin test is sensitive a small amount of blood is needed The blood can be years old (mummified tissues 4000 years old have given positive results!) Diluted blood stains (washed) can still test positive

21 What is the blood type?

22 Determining blood type Blood type is based on an antigen-antibody reaction The RBCs have several antigens on the surface; the three most familiar are A antigen B antigen D antigen (responsible for positive or negative) In reality there are over 256 antigens for more than 23 blood groups!

23 Determining blood type The antibodies in the blood plasma will be the opposite of the antigen on the RBC Blood type Antigen Antibody A A anti-b B B anti-a AB AB none O none anti-a, anti-b

24 Determining blood type When typing blood... The antibody has two binding sites, one on each end Two antigens can attach to one antibody, and one RBC can be attached to several antibodies Clumping (agglutination) will occur

25 Determining blood type 1. The blood sample is placed into three wells, labeled A, B, Rh (antigen D) 2. The appropriate antibody is added to each well (anti-a to well A, anti-b to well B and anti-d to well Rh ) 3. Stir and wait a minute 4. If the blood clumps in a well then that antigen was on the surface

27 What is the blood type?

28 Generalities with blood types Type O is common in indigenous populations (Native American, Aborigines, Latin America) Type A is common in Caucasian populations Type B is common in African American and some Asian populations (Thai) Type AB is common in Japanese and Chinese populations Middle Eastern populations have nucleated RBC Males tend to have more RBCs than females

29 Frequency table ABO PGM EAP Hp A 40% 1-1.8% A 11.2% % B 10% % B 39.5% % O 45% % BA 41.4% % AB 5% % C 0.2% 2-0.3% CA 3.2% % CB 4.6% % % % %

30 Genetics of Blood Type There are 3 alleles that determine the ABO blood types I A, I B, i Type A is either I A I A or I A i Type B is either I B I B or I B i Type AB is I A I B Type O is ii

31 Genetics problems What are the possible blood types for the children of a father with Type A blood and a mother with Type O blood? What are the possible blood types for the children of a father with Type A blood and a mother with Type B blood?

Blood History Karl Landsteiner first typed blood into A, B, AB, O Rh factor was discovered (positive or negative i.e.

Blood History Karl Landsteiner first typed blood into A, B, AB, O Rh factor was discovered (positive or negative i.e. Blood Blood History 1901 Karl Landsteiner first typed blood into A, B, AB, O He was awarded the Nobel Prize for this 1937 Rh factor was discovered (positive or negative i.e. AB+, O- Blood Information At