Blood donation and will screen for antibodies to less common antigens. More testing, including a crossmatch, is usually done before a transfusion. Type O negative is often cited as the "universal donor" but this only refers to red cell and whole blood transfusions. For plasma and platelet transfusions the system is reversed: AB positive is the universal platelet donor type while both AB positive and AB negative are universal plasma donor types. Most blood is tested for diseases, including some STDs. The tests used are high-sensitivity screening tests and no actual diagnosis is made. Some of the test results are later found
Rh blood group system Rh blood group system The Rh blood group system is one of thirty-five known human blood group systems. It is the second most important blood group system, after the ABO blood group system. The Rh blood group system consists of 49 defined blood group antigens, among which the five antigens D, C, c, E, and e are the most important. There is no d ("little d") antigen. Rh(D) status of an individual is normally described with a "positive" or "negative" suffix after the ABO type. e.g. Someone who is A Positive has the A antigen and the Rh(D) antigen, whereas