By Sebastian Restrepo

The Use of Blood in Forensics

Blood is one of the most useful things used in forensics. Not only is it one of the most common physical things of evidence, it is one of the most important piece of evidence used in solving crimes. It helps pinpoint individuals and their relation to the crime. One of the many way blood is useful for scientists is the ABO system, which involves examining the surface of the red blood cell for two antigens known as A and B. These often can predict race of the human.

Teens Life is Saved when Blood Splatter Evidence Proves she could not have Killed her parents

For one "lucky" teen, blood was the "aha" evidence that saved her life. A famous murder case from Idaho put the daughter of a murdered couple on trial. Retired crime lab technician Michael Howard testified that whoever shot Diane and Alan Johnson at close range on September 2, 2003, would have been hit by a "rain" of blood spatter.

However, Sarah Johnson, 18, who faced life in prison for two counts of first-degree murder, did not have her parents' blood on her that morning, according to Howard.

Investigators found out later that Sarah did not kill the two parents, and that the misting pattern of blood indicated that the shooter was wearing Sarah's robe.

Interesting Facts about Blood

  • Blood makes up about 7% of the weight of human body.
  • Blood cells float in a yellow liquid called blood plasma.
  • There are 150 billion red blood cells in one ounce of blood.
  • The most common type of blood in the united states is O Positive, while the least common blood type is AB negative.



Serology is a blood test to detect the presence of antibodies against a microorganism.


Colorless watery fluid of blood and lymph containing no cells and in which erythrocytes and leukocytes and platelets are suspended.


Large Y-shaped Protein produced mainly by plasma cells that is used by the immune system to neutralize pathogens such as bacteria and viruses.


These are toxins or other foreign substances that includes an immune response in the body, especially the production of antibodies.


A red blood cell, contains hemoglobin, which imparts the red color to blood. It can carry oxygen to the body.


ABO is a blood group system. It is what determines what blood type a person has. A,B,O or A- B-.
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This is any type of specific antigen present on the surface of red blood cells.


A colorless cell that circulates in the blood and body fluids and is involved in counteracting foreign substances and disease (a white blood cell)


A small colorless disk-shaped cell fragment without a nucleus, found in large numbers in blood and involved in clotting.
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A red protein responsible for transporting oxygen in the blood of vertebrates. Its molecule comprises four subunits, each conturing an iron atom bound to a heme group.

Blood Factors

Blood factors are the relation with blood clots. There are proteins in the blood that control bleeding. Many different clotting factors work together in a series of chemical reactions to stop bleeding.


An amber-colored, protein-rich liquid that separates out when blood coagulates.