Updated

Guarding against mad cow disease, the American Red Cross said Monday that it will stop accepting blood donations from people who have spent as little as three months in Britain or six months anywhere in Europe.

The Red Cross rules, which will take effect in September, are much stricter than those contemplated by the Food and Drug Administration.

Experts worry that the dueling policies will further confuse the public about the baffling disease. The American Red Cross said Monday that caution is needed given that there is no blood test for the human form of mad cow disease, which has a long latency period.

"In light of tremendous scientific uncertainty, we have to make the best judgment possible," said Red Cross spokeswoman Blythe Kuvina.

The Red Cross estimates that the new rule will make 8 percent of its current donors ineligible, Kuvina said, adding that the organization was already working to increase its pool of donors.

Last year, the FDA banned blood donations by anyone who spent a total of six months in Britain between 1980 and 1996, when that country was the epicenter of the mad cow outbreak.

But with mad cow disease spreading throughout Europe, in January the FDA's scientific advisers recommended banning donations from anyone who spent a total of 10 years in Portugal, France and Ireland since 1980. The expert panel, which included some of the nation's top mad cow experts, concluded that these countries were of most concern, but said the risk there was lower than that in Britain.

In February, the FDA indicated that its policy would closely adhere to the recommendations of its advisers, who argued that the Red Cross' call for tighter restrictions went farther than necessary. The FDA's blood chief, Dr. Jay Epstein, said then that the agency was likely to impose the ban only on travelers to Portugal and France.

Under the Red Cross policy announced Monday, donations will be banned from:

—Anyone who has lived in the United Kingdom for a total of three months or longer since 1980.

—Anyone who has lived anywhere in Europe for a total of six months since 1980.

—Anyone who has received a blood transfusion in the United Kingdom.

The Red Cross, which collects about half of the nation's blood supply, is legally allowed to set stricter standards than required by the FDA. But its blood banks may not say or imply that their blood is safer than those collected by banks following the FDA standards.

Defending the Red Cross' plans earlier this year, Dr. Bernadine Healy, the group's president, called the FDA standards "minimal." If the nation won't import any European cattle, she said, her blood banks should adopt a similar standard.

Healy said she was not implying that the Red Cross standard was better than the FDA's.

"They're making a judgment. We're making a judgment," she said.

Mad cow disease seems to spread to people through eating infected beef. There is no proof yet that it or its human counterpart spreads through blood. But how to protect the blood supply in case the disease eventually hits the United States and proves a real threat is controversial.

Competing blood banks fear patients will perceive the Red Cross policy as safer and thus they will have to follow suit, risking shortages by turning away longtime donors like military families.