|MadSci Network: Medicine|
Unfortunately the answer to your question is still yes, there is a very remote possibility of getting HIV from a blood transfusion. The risk is substantially reduced from before they started testing but there is still some risk. The reason why is that the tests for HIV are not perfect. This relates to not just tests for HIV but for any clinical testing; there is always the potential for false-positive results and false-negative. In fact many clinical tests and over-the-counter tests are intentionally slanted towards being more likely to give a false-positive or false-negative than give a result that could be harmful. For example, home pregnancy tests are more likely to be false-positive than false-negative, based on the fact that if a woman gets a negative result and is really pregnant than she might engage in behaviour that could be harmful to the fetus (like drinking alcohol). Similarly, testing blood for HIV is slanted towards giving a false-positive rather than a false-negative because the consequences of a false-negative would be to give HIV-infected blood during a transfusion. However, as I said no test is perfect and there is always a possibility that a false-negative result could occur. So the risk is substantially reduced. However, there are other blood-borne diseases around (such as Hepatitis C) and new ones may yet be discovered. Currently the recommendations of most competent doctors I've spoken to (and I believe the AMA as well) is to bank your own blood if you are scheduling elective surgery that may require a blood transfusion. There is nothing to be done about emergency situations, however, but the benefits of a blood transfusion in that situation far outweigh any risk of HIV or Hep C. In the aftermath of HIV and Hep C, the best that can be said is that the blood supply should never be viewed as "completely" safe, however, it is still an enormous benefit to society and all people should still be encouraged to donate.
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