US health officials are recommending an end to America's lifetime ban on blood donations from gay and bisexual men.
The Food and Drug Administration said it favoured replacing the outright ban with a new policy barring donations from men who have had gay sex in the previous year.
These guidelines are supported by research and would put the US in line with other countries including the UK, Japan and Australia, according to an AP report.
The lifetime ban dates back to the first years of the Aids crisis and was intended to protect the blood supply from a little-known or understood disease and how it was spread. Many medical groups including the American Medical Association say that this strategy is no longer supported by science.
Gay activists say the lifetime ban is discriminatory and enforces negative and biased stereotypes of homosexual and bisexual men.
FDA Deputy Director Dr. Peter Parks refused to give a timeframe for completing the process but said, "we commit to working as quickly as possible on this issue."
All blood donations are screened for HIV but the test only detects the virus after it's been in the bloodstream for around 10 days. That allows a brief period of time when the virus that causes AIDS can go undetected.
Parks, deputy director of the FDA's Centre for Biologics Evaluation and Research said he expects about half of the would-be blood donors who are currently kept away because they have had sex with other men would become eligible to donate.
He also revealed that the FDA are working on creating a new system to monitor the safety of the blood supply. Currently the American Red Cross detects and discards hundreds of units of donated blood which contain the HIV virus each year. The chance of finding an HIV-contaminated unit in the blood supply, he said, is 1 in 1.5 million.
Men who have had sex with other men represent about 2% of the U.S. population, yet account for at least 62% of all new HIV infections in the U.S, according to government figures.
Some LGBT groups criticised the new policy, believing it still stigmatises gay men. "Some may believe this is a step forward, but in reality, requiring celibacy for a year is a de facto lifetime ban," said a spokesman for Gay Men's Health Crisis, a nonprofit organisation that supports Aids prevention and care.
Health groups and organisations have been calling for an end to the ban including the Red Cross, the National Haemophilia Foundation, the American Association of Blood Banks, and America's Blood Centres who called the ban "medically and scientifically unwarranted."
In 2013, the American Medical Association voted to oppose the policy, with one board member calling the ban "discriminatory."
Currently, men and women of any sexual orientation are barred for donating blood for one year after having sex with someone with HIV, with a commercial sex worker or with an intravenous drug user.