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
Hh blood group member of the ABO blood group system (unless some other blood factor gene, such as Rh, is incompatible), but they cannot receive blood from any member of the ABO blood group system (which always contains one or more of A, B or H antigens), but only from other people who have Bombay phenotype. Receiving blood which contains an antigen which has never been in the patient's own blood causes an immune reaction due to the immune system of a hypothetical receiver producing immunoglobulins not only against antigen A and B, but also against H antigen. The most common immunoglobulins synthesized