Should men who have slept with men give blood?
Two prominent HIV scientists from Canada have called for an end to the blanket ban on blood donations from men who have had sex with men.
They believe it is out of step with science and is reducing the number of healthy donors whose blood could be saving lives.
The issue is one the UK is currently examining, amid growing calls around the world for change.
Many developed countries - including the UK - have a lifetime ban on blood donations from men who have ever had sex with other men, even if the encounter took place many years earlier.
The policy was introduced in the early 1980s as the threat of HIV/Aids emerged.
But writing in the Canadian Medical Association Journal, Mark Wainberg and Norbert Gilmore note that the highly sensitive procedures now routinely used for testing mean it would be very hard for infected blood to slip through.
It was time, they said, to consider scrapping the old policy of "indefinite deferral" and look at asking men to wait between one and five years after having sex with another man before giving blood.
"The current policy is counterproductive in terms of loss of donors, loss of good will, student protests, donor boycotts, among other negative effects," they write.
"We believe that any potentially negative consequences of a change in deferral would be offset by the benefits."Transmission time
Opponents of the lifetime ban point to new testing techniques which are able to detect the HIV virus in the blood after as little as 12 days - down from three to six months previously.
Thus a "window" where infected blood might unknowingly enter the supply system remains, but it is a very short one. And opponents of the lifetime ban also point to the moral issue of double standards.
End Quote John Kerry US Senator
Not a single piece of scientific evidence supports the ban”
For instance, a woman who has slept with a man who himself sleeps with men may, in some countries, donate after a year - even though the man is permanently barred - however long after the event he tries to donate.
For those opposing the lifetime ban, barring all men who have had sex with other men is tantamount to making a homophobic presumption of blanket contamination.
They see it as out of step with both science and social attitudes and want men to be judged individually, according to their lifestyle.
A number of countries, including Argentina, Australia and Japan, have already lifted lifetime bans and allowed men to donate, on the condition that they have not had sex with another man for a year.
In the US there have been calls for the policy to be reviewed. Earlier this year, a group of senators wrote to the Food and Drug Administration asking for the ban to be lifted. "Not a single piece of scientific evidence supports the ban," said John Kerry, the former presidential contender.
But those who oppose lifting the ban say the protection of end-users from a risk - however theorectical that may increasingly be - must take precedence.
It is a view held by the authorities in Germany where new guidelines restating the exclusion of men who sleep with men are due to be published soon.
Between 2000 and 2007 there were five cases of German patients being infected with HIV through blood transfusions, two of which could be traced back to men who had slept with men.
Friedrich-Ernst Dueppe of the German Red Cross said:"It's not many, but think about this. In Germany we don't allow people who were in the UK for six months between 1980 to 1996 inclusive to give blood because of the fear of Creutzfeldt Jakob Disease.
"This is a purely hypothetical risk - we've never seen a case of that happening here.
End Quote Thomas Attnaes Geblod, Sweden
The number of men we are talking about is going to be small”
"But we know there is a genuine risk of HIV transmission from men who sleep with men, however good the tests are now. The right of the receiver to be protected from risk as far as possible is always going to trump the right of a potential donor to give."
The issue is about to be examined in the UK, where the Advisory Committee on the Safety of Blood, Tissues and Organs is reviewing the current donor ban. It is due to present its findings later this year.
Among the evidence it will look at is the rate of HIV infection rates - rising in both homosexual and heterosexual communities in the UK, but with new rates of infections acquired within the country itself still far higher within the gay community.
And there is not - and has not been for many years - a shortage of blood in England, according to the NHS body which oversees blood and organ transplants.
The Terence Higgins Trust supports the review, but urges everyone to adhere to the rules in the meantime.
Victoria Sheard, policy manager at Terrence Higgins Trust, said: "The vast majority of blood services around the world do not allow men who have sex with men to give blood, although several countries, including Canada, are now examining alternatives to a lifetime ban.
"Here in the UK, the National Blood Service is in the process of a comprehensive review to see whether it would be safe and pragmatic to lift or amend the ban. Until any further decision has been made, we are asking people to abide by the current restrictions.
"There are now over 450 rules guiding blood donor selection in the UK. The question is not whether restrictions should exist but whether the right ones are in place.
"It's important that people are reassured that all the evidence has been examined and that any restrictions are made on the basis of evidence and not political pressure or wishful thinking."Political statement
While lifting the ban may be fairer, changing the rules has the potential to bring its own problems, as Sweden has discovered.
It was due in March to become the latest country to allow donations from men who have not had sex with other men within the last year.
However it has now been forced to postpone the change.
Thomas Attnaes of Sweden's blood agency said: "There are a lot of practical problems, and now we think it will be at least another 18 months before this happens.
"In part this is because we have been asked to set up interview rooms so that we can really talk to the donor - that's hard when a lot of our facilities are very small, or mobile.
"But this isn't really about blood shortages - we have our ups and downs, but the number of men we are talking about is going to be small. It's not going to change much - it's more a political statement."