WASHINGTON, May 20 (Reuters) - U.S. health officials are seeking to relax blood donation rules for some people who initially tested positive for hepatitis B, which could clear hundred of thousands of new donors, according to documents released on Tuesday.

People whose blood showed signs of the liver-swelling virus after repeated tests are currently banned from ever donating blood, even if medical tests later showed they were not infected.

But in a draft proposal, the U.S. Food and Drug Administration (FDA) said that a new, more specific test could help determine whether donors who initially fail a first test are truly infected and suggested they be allowed to give blood after an 8-week waiting period.

While the FDA said chances of someone repeatedly testing falsely positive for hepatitis might seem rare, older less specific tests that checked for antibodies to hepatitis B core antigen, or anti-HBc, kept many possible donors from giving blood.

"It is estimated that as many as 21,500 potentially eligible donors were deferred annually in the late 1980s and 1990s because of false positive anti-HBc results," the FDA said, adding that more than "200,000 donors could be eligible for reentry."

Potential blood donors are closely screened for hepatitis and other infections such as the AIDS virus as well as drug use and other risky behaviors to prevent the spread of disease.

Hepatitis B is transmitted through blood and other body fluids and can cause jaundice, muscle aches, nausea, fatigue and, in rare cases, liver failure.

Initial symptoms can clear up after a few weeks, but it can take up to six months for patients to fully recover from a serious bout. Some patients can also develop a chronic case of hepatitis.

The FDA is seeking public comments on its proposal before making it final. The draft is posted on its Web site at http://www.fda.gov/cber/gdlns/reentrybld.htm. (Reporting by Susan Heavey; editing by Anthony Boadle)

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