- Different blood types were not recognized until 1875 and they were not organized into groups until 1900. In 1901, Karl Landsteiner discovered the ABO blood typing system. This was a revolutionary break through for forensic science. From then on, blood typing was used to help eliminate potential suspects in various crime scenes, according to "Forensics Demystified" by David Fisher, Barry Fisher and Jason Kolowski.
- Red blood cells have antigens (substances that produce antibodies to fight infections). Landsteiner recognized several types of antigens when he separated red blood cells from plasma in a centrifuge (a device that spins blood samples). Landsteiner found two distinct reactions (repelling and clumping) when he added red blood cells from other individuals, according to "Serology: It's in the Blood" by Katherine Ramsland. These were labeled A (when antigen A is present, antigen B is absent and anti-B antibody is present) and B (when antigen B is present and antigen A is absent). The third reaction was labeled O. This came to be known as the ABO blood typing system.
- In 1932, Dr. Leon Lattes invented a way to test for antibodies in dried blood flakes. This was an important discovery in that it was the first time that dried blood could be tested. Furthermore, he also developed a procedure for applying blood testing to stains on fabric, according to "Serology: It's in the Blood."
- In 1940, Landsteiner discovered the Rhesus factor along with Alexander Wiener of the New York City's Office of Chief Medical Examiner. The Rhesus factor refers to the five main antigens found in blood (on the surface of red blood cells). The discovery of the Rhesus factor led to many developments in forensic blood techniques, according to "Forensics Demystified."
- Later history of blood serology concentrated on further individualization of blood work. In particular, scientists worked on developing techniques for identifying the person's gender through the use of an enzyme/protein profile. As a result, current blood typing includes testing for many types of enzymes and proteins. In fact, as of today, scientists have found more than 150 serum proteins and 250 cellular enzymes varieties, according to "Serology: It's in the Blood." Another major breakthrough was the application of DNA technology. As result, it is now more accurate to match DNA from a blood sample at a crime scene than it is to create an entire blood profile (using enzymes and proteins). Yet the blood profile is still useful in offering clues as to the gender and blood type of the individual.