Forensics History of Blood Analyzing

Blood evidence analysis has a long history.

In the field of forensic science, blood is one of the most crucial forms of evidence. Blood evidence can help identify perpetrators by matching bloodstains with a reference sample. In order to obtain an identity based on blood, forensic scientists need accurate and reliable blood analysis methods. Technologies that exploit DNA have improved the reliability of blood analysis. Before DNA, blood analysis used methods that were major breakthroughs in forensic biology.

Presumptive Tests

In order for forensic scientists to analyze blood samples, they first must determine whether the evidence found is blood. Presumptive tests are first performed to screen for the possibility of blood. Chemicals that change color in the presence of blood have been used in the past and are still used today. Historically, tests developed by Oskar and Rudolf Adler used benzidine, which is now known to be a carcinogenic. Therefore, other chemicals, such as Luminol or leucomalachite green, are used to test for the presence of blood. Crystalline tests have a long history in forensics as well. The Teichman test and the Takayama test, both of which cause crystallization in the presence of heme structures (found in blood), were discovered in 1853 and 1912 respectively, and are still used today.

Human Blood Identification

Blood analysis also involves determining whether the blood is human. An immunological method involving antigens and antibodies was discovered by Paul Uhlenhuth, a German biologist, in 1901. He found that serum from a rabbit that was injected with egg protein would form a cloudy substance when mixed with egg white because the serum had egg protein antibodies. He called this substance precipitin, which led to the current precipitin test. When a blood sample is placed with antibodies against human proteins, a precipitin will form if the blood is human.

ABO Blood Typing

Perhaps the most well-known blood analysis method is that of the ABO blood type. In 1901, Karl Landsteiner discovered and named the ABO types. He discovered that everyone has either an A, B or O blood type, based on the type of antigens on the individual's red blood cells. Historically, using antibodies, the ABO typing test could determine the blood type of the evidence, which helped narrow the list of possible matches, but it could not identify an individual.

Blood Proteins

In 1940, Landsteiner discovered the Rh factor, labeling people Rh positive if they had the antigen or Rh negative if they did not. This helped isolate individuals even further. In 1949, British scientists discovered a chromosome-related structure in female blood, called the Barr Body, that differentiated female blood from male blood. Since then, hundreds of other discriminating proteins and enzymes in the blood have been discovered that help identify an individual. This allows scientists to testify with a higher sense of probability that a particular bloodstain matches a particular individual.

DNA

In 1985, Alec Jeffreys developed the first DNA profiling test involving RFLP analysis, or restriction fragment length polymorphism. The DNA method is much more reliable than drawing up a blood profile made up of the many proteins and enzymes. The RFLP method has since been replaced by the more popular STR (short tandem repeats) analysis.

References

• TruTV: Serology
• Austin Peay State University: Forensic Serology
• "Forensic Science Handbook"; Richard Saferstein; 2002