Dna Blood Test
Before 1901 when the DNA blood test was discovered blood transfusions very often went wrong, causing serious problems and even death in patients who desperately needed blood. This is because medical professionals were unable to match the right blood types together (they didn't even know different blood types existed!) and so blood 'clumping' often occurred between incompatible types. Blood types A, B, which contain A and B antigens respectively, are incompatible together, but blood type AB can accept blood from any type. Blood type O has no 'antigens'; cells provoking a specific immune response, and can therefore be used for donation to any other person. Clumping is an immune response to blood with different antigens, so if the two blood types' antigens match then there will be no response.
The test itself involves taking a simple blood sample and then mixing that sample with samples of blood from each of the groups. Using a chart, scientists or medical professionals can determine which blood group you are, depending on which of the samples your blood clumps or doesn't clump with. This is often kept on record so that if you are found unconscious, medical professionals can start looking for a blood transplant donor as quickly as possible.
Today, blood typing or DNA blood tests are far more in depth and can identify more than four blood types. Within those four other types can be found, such as Duffy A and B or rhesus positive or negative. They're used for a huge number of reasons too, besides working out a person's blood type for donation or transplants, so find out your blood type and hang on to the knowledge; you never know when it will come in useful.