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
Jehovah's Witnesses and blood transfusions place patients at heightened risk for reduced long-term survival." The study also stated that "Survival estimates of Witnesses were 86%, 69%, 51%, and 34% at 5, 10, 15, and 20 years after surgery, respectively, vs 74%, 53%, 35%, and 23% among non-Witnesses who received transfusions." Bloodless medical and surgical techniques have limitations, and surgeons say the use of various allogeneic blood products and pre-operative autologous blood transfusion are appropriate standards of care for certain patient presentations. The Watch Tower Society states that in medical emergencies where blood transfusions seem to be the only available way to save a life, Jehovah's