The blood shortage around the nation has worsened in recent months as a result of new federal restrictions on donor blood, created to prevent the transmission of mad cow disease, health officials said.
The Princeton Medical Center has been forced to turn away about five to 10 donors per month because of the legislation, translating to an estimated 10-percent drop in donations, said Rao Andavolu, director of PMC's blood bank.
The decrease in donations has neared 20 percent in New York and New Jersey. Imported blood from Europe, now prohibited, once comprised a considerable portion of the blood supply.
"We shouldn't be waiting for a disaster to happen," Andavolu said. "We need to create a culture of blood donation, of social responsibility."
The FDA guidelines, established in June, recommend restricting anyone who had spent at least three months in the United Kingdom from 1980 to 1986 from donating blood. Also considered ineligible are those who have lived five years or more in Europe since 1980.
Stricter guidelines will be released this October, Andavolu said.
The American Red Cross, responsible for half the nation's blood supply, established deferral policies that are more stringent than the FDA recommendations.
Scott Murphy, chief medical officer at the Red Cross center in Philadelphia, said the country has enough blood to last only two days if donations were to stop entirely. Medical centers are not ready to handle a major national crisis, he said.
The most pressing concern is not that blood banks are overflowing with infected individuals but that not enough donors give blood in the first place, Murphy said.
In light of these concerns, health officials, such as Andavolu, have urged New Jersey lawmakers to allow younger people to give blood. As a result, the minimum age to donate blood without parental consent was lowered from 18 to 17 in September.
In the past several weeks, outbreaks of West Nile virus, commonly spread by mosquitoes, have compounded the threat to the blood supply. There is no screen for the virus, and there have not been any policy changes for donors.
Murphy said he is worried about the public response to recent warnings of blood shortages.

"I think and pray that the public understands that it's simply impossible to contract West Nile through donating," he said.
For those needing surgery, the risk of contracting the virus is negligible.
Pat Wann, spokeswoman for the Community Blood Council of New Jersey, still emphasizes the need to take extra precautions.
A donor exhibiting any sign of sickness, even if they claim to have allergies, is grounds for automatic deferral.
"West Nile symptoms are cold-like, so we can't take a chance," she said.
Because of the low blood supply, anyone who can donate should, Andavolu said.
About 5 percent of eligible Americans donate, he said, but if 7 percent were to do so, there would no longer be a shortage.
Russ Goldman '03, president of the University's Blood Drive Committee, said he is determined to attract more students to the cause. He is working with Panera Bread to create a coupon incentive for participants of this November's blood drive.
Efforts like these might help the dire blood shortage, but more regular donors are needed to increase the supply, health officials said. With respect to current situation, Murphy is frank.
"It's like driving across Death Valley with a tank of gas only a quarter full," he said.