The victim of a car accident can require as many as 100 pints of blood—that's blood from 100 generous donors across the country, meticulously matched for blood type and screened for diseases. More than 38,000 blood donations are needed daily in the U.S., but only 38 percent of Americans are eligible to donate blood, and of those, only 8 percent actually do.

The list of eligibility criteria that a donor must meet is long, ranging from simple characteristics such as age and weight requirements to more complex ones surrounding medical and travel history. Among them is the risk for human immunodeficiency virus (HIV) infection or acquired immunodeficiency syndrome (AIDS). Certain factors thought to increase this risk, including illicit intravenous drug use and, if you're a man, having had sex with another male even once since 1977, currently prohibit you from ever donating blood.*

But AIDS research pioneers from the Jewish General Hospital and McGill University in Montreal think the ban is outdated. In their report, published May 25 in the Canadian Medical Association Journal , they call for a change in policy, which was created by the U.S. Food and Drug Administration (FDA) in 1983—before HIV/AIDS screening tests were available. "Today's technology makes it almost impossible for HIV to slip through, and the total ban puts a huge burden on blood agencies and the blood supply," said lead author Mark Wainberg, in a prepared statement. He helped in the discovery of 3TC, one of the first drugs to control HIV. "We constantly have blood shortages that would not occur, perhaps, if we had a more reasonable policy."

History of the ban

In the spring of 1981 cases of an unusually aggressive form of Kaposi's Sarcoma, a benign tumor that normally affects older people, and a rare lung infection called pneumocystis carinii pneumonia (PCP) began to be reported among gay men in New York City and California. To learn more about the transmission of this new, seemingly acquired form of immunodeficiency, the U.S. Centers for Disease Control and Prevention (CDC) formed a Task Force on Kaposi's Sarcoma and Opportunistic Infections. In July task force coordinator James Curran told The New York Times there was no apparent danger to nonhomosexuals. But by December, cases of PCP were also turning up in illicit intravenous drug users.

By the summer of 1982, 452 cases or the new disease in 23 states had been reported to the CDC. Haitians and hemophiliacs also appeared to be vulnerable, resulting in the moniker, the "4-H club" (for homosexuals, heroin addicts, Haitians and hemophiliacs). That December a 20-month old child who received multiple blood transfusions died from AIDS-related infections. The first cases of possible mother to child transmission were also reported.

Evidence that the acquired immunodeficiency syndrome (AIDS, the term for the disease officially adopted by the CDC in September of that year) could spread through blood transfusions caused panic. And in January 1983 a CDC-held public meeting led to a consensus to ban blood donation by men who have sex with men. The rationale: AIDS was a blood-borne disease and the majority of cases had occurred in homosexual men.

"The 1983 ban has hung on so long, unfortunately, because many people became infected by HIV in the early '80s through blood transfusions, and they have mounted continuing pressure on the blood agencies to maintain the ban," Wainberg said in a prepared statement. "While we can sympathize with them, this no longer makes sense in 2010, and with each passing year it makes less sense."

Since 1983 the number of heterosexually transmitted infections has increased dramatically, accounting for about a third of total infections in the U.S. in 2006, according to CDC estimates. But up to 47 percent of all HIV infections (62 percent in men) are still transmitted through male-male sexual contact, according to CDC statistics from 2007. Nevertheless, current blood screening techniques can effectively eliminate the risk of HIV-infected blood, regardless of whether it came from a donor who has had such contact in the past year or the past 33 years.*

Weighing the risks and benefits

After a pint of blood is collected, it is processed into its transfusible components: plasma, platelets and red blood cells. A dozen tests are then performed to establish the donor's blood type and screen for infectious diseases. Since 1985 the American Red Cross has used enzyme immunoassays to test for antibodies to HIV-1 and HIV-2. A positive result is confirmed using at least one additional technique to identify virus-specific antibodies.

Whereas the number of AIDS cases that resulted from transfusions before screening measures were implemented is unknown, CDC-reported mathematical estimates based on HIV-positive donation rates in 1985 suggest that as many as 7,200 transfusion recipients could have received infected blood components. Antibody-based screening measures "virtually eliminated" the risk of transmission by transfusion, which now sits at about one in two million, according to the Red Cross.

In 1999 the Red Cross added another technique to its screening process call nucleic acid testing, which detects the virus's own genetic material using the same gene-amplifying techniques used to test for paternity. The test reduces the amount of time that a person's tested blood could yield a false negative, called the "window period," from three to six months with antibody screening alone (because it takes time for the body to produce antibodies to the virus) to about 12 days. "This "window period" is often the most dangerous time for transmission, because the host may be unaware that he or she is carrying the virus and might unknowingly donate infected blood," Wainberg and colleagues report. But they argue that improvements in screening technology make the current total ban on donors who have had male-male sexual contact pointless, and that the temporary one-year ban implemented for heterosexuals with multiple partners should also be applied to men who have sex with men. Currently, women who have had sex with men banned for life are only prevented from donating for a year.

The major benefit of allowing men who have sex with men to donate blood after a reasonable temporary ban would be a boost in the blood supply, the authors say. "In the United States it has been estimated that a five-year deferral would lead to an increase of 71,400 donors, whereas a one-year deferral would lead to an increase of 139,000 donors," they report. They also say blood clinics would stop losing healthy donors who refuse to donate because they find the current bans offensive. "When a discriminatory policy isn't justified by the science, it leads to controversy," Wainberg said in a prepared statement. "We've seen protests and boycotts of blood drives on Canadian campuses, so I think the blood agencies would be better off if they agreed with us. I suspect, honestly, that many of them already do, in private."

But protecting patients who receive blood is the priority for agencies like the Red Cross. "More important than increasing the donor pool is ensuring the safety of the blood supply," says Red Cross spokesperson Molly Dalton. The agency has tried to get the FDA to reexamine the guidelines as new scientific evidence becomes available, Dalton says. But the latest discussions, which took place in May 2007, did not lead to any changes. "We’re continuing to work with the [American Association of Blood Banks] to ensure that policies are fair and based on scientific evidence," Dalton notes. The policy, she adds, will be reviewed again at a meeting this summer.

*Correction (6/2/10): These sentences were edited after publication to correct an error.