Originally Answered: Why can't gay people donate blood?
The FDA, particularly the Center for Biologics Evaluation and Research (CBER), has recently voted to maintain an indefinite deferral for any male-sex-male (MSM) that has occurred, even once, since 1977. However, the American Red Cross and America's Blood Centers have recommended decreasing the deferral period to one year from last contact. A similar change was just enacted in the United Kingdom.
Unfortunately, many do not understand the rationale behind the deferral guidelines. CDC data has consistently identified MSM as a significant risk factor for transfusion-transmissible diseases, especially Hepatitis B and HIV. As with other high risk activity, the guidelines are in place to protect not only the recipients of blood components, but also the collection, testing and nursing staff of blood centers and hospitals.
While some consider this discrimination, it is in reality a response to epidemiological data. Current blood donation screening using HIV Nucleic Acid testing (PCR) may detect viral RNA as early as 7-10 days post-exposure. HIV antibody testing, used in conjunction with NAT, can detect infection after 12-21 days post-exposure. It is this "window period', the time between infection and detection, that the FDA is concerned about. Though window-period donations are rare, the first case of post-transfusion HIV since 2002 was recently reported in the publication listed below:
CDC "Mortality and Morbidity Weekly Report" October 22, 2010 / 59(41);1335-1339
Specifics on the donor indicate unreported MSM activity over many years.
Until pathogen inactivation technology has been perfected to treat donated blood components for transfusion-transmissible diseases, donor questionnaires and screening tests provide the best chance for a safe blood supply
Please see the FDA link below for FAQ concerning MSM.