The Food and Drug Administration on Tuesday ended the lifetime ban on blood donations from men who have sex with men .

But the agency said it would continue to bar donations by men who have had a sexual encounter with another man in the previous year, disappointing prominent gay rights groups and HIV/AIDS researchers, who called the yearlong waiting period medically unnecessary and unscientific. The FDA said the change "will better align the deferral period with that of other men and women at increased risk for HIV infection."

The one-year deferral notion constitutes symbolic progress, but is not any more warranted than a lifetime ban," wrote Dr. Eli Adashi, professor of medical science at Brown University's Warren Alpert Medical School, in an email to HuffPost.

The 31-year-old ban on donations from gay and bisexual men had its roots in the AIDS fear that was pervasive when the disease first appeared in the nation's blood supply . Since then, HIV testing has gotten faster and more accurate . Additionally, testing of donated blood for HIV and other diseases is routine.

Over the years, pressure mounted for the FDA to change the ban. The American Medical Association recommended that gay and bisexual men be evaluated individually, and that risk be assessed through behavior, not sexual orientation.

The lifetime ban on blood donation for men who have sex with men is discriminatory and not based on sound science, said Dr. William Kobler, an AMA spokesman.

Members of Congress spoke out against the ban .

Gay rights groups also advocated that the FDA drop the gay blood ban, and replace it with screening questions that address specific risky sexual behaviors regardless of sexual orientation or gender.

Aspects of such a system have been in place in Italy since 2001. There, potential blood donors are assessed individually with questionnaires and face-to-face interviews with practitioners.

Adashi co-authored an op-ed in the July issue of The Journal of the American Medical Association that argued a 12-month deferral on donations from gay men is equally arbitrary to a lifelong ban.

Sexual orientation is not a disqualifier; instead, sexual orientation is one component of individualized risk assessment, Adashi wrote. Research suggests that Italy's new policy hasn't led to a disproportionate increase in HIV-positive blood donations from gay men.

The FDA shift still leaves a large swath of gay men -- those who only have sex with HIV-negative partners or practice safe sex with HIV-positive partners -- unable to donate blood. At the same time, people who may be at risk for HIV are not barred from donating .

Beyond the discriminatory nature of the ban on donations, there is a real need for more blood.

The Williams Institute at the University of California, Los Angeles, which studies LGBT issues, has calculated the number of men who would likely donate, and the pints of blood that would become available, under three scenarios: completely lifting the ban, a 12-month deferral, and a five-year deferral.

As you can see, a 12-month deferral excludes thousands of potential donations from the nation's blood supply.

The risk of getting HIV from a blood transfusion is incredibly low. According to the FDA, one in 2 million cases are acquired through transfusions.