Serology and Forensics Blood Typing And Blood Splatter Analysis
What is blood?
Blood is connective tissue. It is composed of a sticky fluid called PLASMA
Plasma is mostly water but it also has other substances dissolved in the water.
Proteins: antibodies, clotting proteins
Salts and ions: calcium, sodium chlorine
Circulating wastes and nutrients: glucose, lipids, hormones, and wastes
40% of blood volume is actually occupied by cells
Leukocytes: only about 1% of the cells. Defend the body against invasion
Platelets: fragments of bone marrow cells that help in blood clotting.
Erythrocytes: Red blood cells. 5 billion of these cells in 1 ml of blood.
Shaped like a flat disk with a central depression on both sides.
Hemoglobin carrying oxygen makes them red.
Who discovered blood typing? In 1901, Karl Landsteiner reported that blood had TYPES. By matching these types one could achieve success in blood transfusion.
How does blood typing work?
ABO Blood Groups
A reaction outside the body between like antigens and antibodies results in Agglutination where the blood cells clump together.
A reaction within the body between like antigens and antibodies results in Hemolysis of the cells (they burst).
Blood typing detects sugars that act as recognition markers on the surface of our own erythrocytes (red blood cells, RBC’s).
These sugars are recognized by our own immune system and are called cell surface antigens.
There are THREE possible genes to code for the markers:
Three possible genes to code for the markers
Since you can get ONLY ONE gene from each parent, each individual can only have two genes to code for the sugar markers.
Genetic possibilities Mother Father A O B O AB AO BO OO
What are the possible Blood Groups ? ABO
TWO facts you need to know to interpret how the genes combine to give blood groups.
Gene 1A and Gene 1B are co-dominant. Both sugars are equal in their presence on the RBC’s
Gene 1i codes for no sugar, so it is dominated by both 1A and 1B.
The Four Blood Types are: Blood types Sugar Gene combinations A A 1A1A, or 1A1i B B 1B1B, or 1B1i AB Both A and B 1A1B O None 1i1i If someone has blood type AB, could one of their parents Have blood type O?
Blood Groups in average Population
The various ABO blood groups occur in the average population of the US show in the diagram to the left.
These percentages vary with different ethnic groups.
Discovered (1946) by Karl Landsteiner, Phillip Levine, and Alexander Weiner and their research on the Rhesus monkey, hence the name Rh factor.
Three genes ( C, D, and E ) code for the Rh antigens present on the RBC cell membrane.
Rh Factors Blood Types Based on Rh Factors
Rh+ Rh antigens are present on the RBC’s
Rh- Rh are not present on the RBC’s.
85% of Americans are Rh+
More Rh Factors
Normally the plasma does not contain Rh antibodies.
Rh negative individuals that receive Rh+ blood can have their immune system develop Rh antibodies that will remain in the blood.
Erythroblastosis fetalis (Hemolytic disease of the newborn)
A Rh negative mother may be exposed to the Rh antigen from the blood cells of the Rh positive baby during pregnancy or at the time of birth.
If the Rh + blood cells enter the Rh - mother’ blood the mother’s immune system may become sensitized and produce antibodies against Rh + blood antigens
In subsequent pregnancies, these antigens may cross the placenta and causes the hemolysis of the Rh + blood cells in the fetus.
What Happens and What Can Be Done?
The Rh positive baby will become anemic.
This can be avoided by injecting the Rh negative woman with antibodies (RhoGAM) during each pregnancy and within 72 hours after birth of each Rh positive baby.
The injection of antibodies into the woman inactivates the Rh antigens on those blood cells that might have entered the mother’s blood and prevents her body from activating her immune system.
How does blood typing work?
Your blood is not attacked by your own immune system because the sugar markers are recognized by your own body.
However, if a type A person receives a transfusion from a type B person, the Type A recipient’s immune system will recognize the type B RBC’s as foreign and attack.
Antibodies are proteins that “ tag ” foreign markers for destruction. The foreign blood cells literally clump together as the antibodies attach to them.
This clumping can be fatal in the body, but it is also the basis for typing blood.
+ Type B blood
Other Examples Blood Donor Type Antigen Antibody Clump? A A Anti-A YES O None Anti-A NO Why are Type O people called universal donors? What would happen if you gave a type O person, type B blood? Who is the universal recipient?
Blood Splatter Analysis
The location, distribution, and appearance of bloodstains and spatters may be useful for interpreting and reconstructing the events that may have occurred in a crime.
A thorough analysis of the position and shape of blood patterns with respect to their origin and trajectory must be determined.
Stain Patterns of Blood
The harder and less porous surface
The less spatter results.
Direction of travel of blood striking an object.
Pointed end of a bloodstain always faces its direction of travel.
Impact of angle
Look at degree of circular distortion of the stain. A drop of blood striking a surface at right angles gives rise to a nearly circular stain. As the angle decreases, the stain becomes elongated in shape.
Stain convergence on a two-dimensional plane.
Can be established by drawing straight lines through the long axis of several individual bloodstains. The intersection or point of convergence of the lines represents the point from which the blood emanated.
Blood Splatter at Crime Scene
Photos of splatter patterns are important
Close-up photos of individual drops can reveal critical information
There may be more than one general pattern.
Shape and size of drops should be recorded with micro scale visible in photo.
Blood itself needs to be collected.
Velocity of Splatter
Pattern should reveal the velocity of the droplets.
The smaller the drops the faster they were moving.
A fog of tiny droplets indicates high velocity most certainly a gunshot or an explosive device.
Many types of blood splatter
In the field there may be several wounds, all with their own pattern.
Traveling drip patterns
Result from blood that falls from a wounded person or person that has blood on them
Bizarre splatter patterns
Droplets flicked from blood soaked hair of a running person.
Weapons carried through scene especially blunt force weapons and knives can leave their own drip pattern.
Patterns reflects the beating of a heart.
In this lab you will be using simulated blood to determine blood types
You will first use known blood types and look at the effects when adding antibody A or antibody B.
You will then have unknowns to determine what blood type it is.
Record all your work on the data sheets.
Make sure you answer all questions, and clean up when done.
Genge, N. E., “The Forensic Casebook”, Ballantine Books, 2002
Lee, Henry, “Crime Scene Handbook”. Academic Press, 2001.
Saferstein, Richard, “Criminalistics an Introduction to Forensics Science”, Prentice Hall, 2001.
Google Image Search, Blood typing and splatter analysis.