Isn't the HIV test accurate enough to identify all HIV positive blood donors?
HIV tests currently in use are highly accurate, but still cannot detect HIV 100% of the time. It is estimated that the HIV risk from a unit of blood has been reduced to about 1 per 2 million in the USA, almost exclusively from so called "window period" donations. The "window period" exists very early after infection, where even current HIV testing methods cannot detect all infections. During this time, a person is infected with HIV, but may not have made enough virus or developed enough antibodies to be detected by available tests. For this reason, a person could test negative, even when they are actually HIV positive and infectious. Therefore, blood donors are not only tested but are also asked questions about behaviors that increase their risk of HIV infection.
Collection of blood from persons with an increased risk of HIV infection also presents an added risk to transfusion recipients due to the possibility that blood may be accidentally given to a patient in error either before testing is completed or following a positive test. Such medical errors occur very rarely, but given that there are over 20 million transfusions every year, in the USA, they can occur. For these reasons, FDA uses a multi-layered approach to blood safety including pre-donation deferral of potential donors based on risk behaviors and then screening of the donated blood with sensitive tests for infectious agents such as HIV-1, HIV-2, HCV, HBV and HTLV-I/II.
