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Friday, July 09, 1999

Blood pressure
A life-saving resource may dry up because a remote risk takes precedence

Howard Fienberg
National Post

A photo of blood vials, with a man and woman looking on.
 
Consider this situation: Your child is hospitalized. She needs a blood transfusion, fast. But the doctor informs you the blood is not available. A shortage exists because many donors have been turned away and old stockpiles disposed of -- all precautionary measures to protect your family from the theoretical risk of infection from a poorly understood disease that might or might not be transmitted by blood. Is this a sound trade-off?

Unfortunately for Canadians, this scenario is no longer hypothetical. Very soon, everyone will have to confront the very imminent risk that a proven life-saving resource may dry up because a remote risk has taken precedence in health policy. According to news reports, the blood supply has been reduced to almost nothing and frightened parents are making public pleas for more blood donors to step forward to save their children. "This is the scariest I've ever seen the blood levels," says a spokesman for the Canadian Blood Services.

The disease in question is Britain's human version of mad cow disease (nvCJD), no trace of which has ever been found in Canada. But travellers to the Old Country (22% of blood donors) just might have consumed contaminated beef, which just might cause nvCJD in humans, which just might get conveyed via their blood stream into the Canadian blood pool, which just might lead to the infection of the little girl needing the transfusion. Too much of a chance to take, apparently.

Canada's blood supply crisis may be worsened now, and for the future, by the plans of the Canadian Blood Services (CBS) and Hema-Quebec (HQ) to ban Canadians who have spent more than six months in Britain since 1980 from donating blood. They are also considering similar moves for visitors to France. This would eliminate at least 4% of the donor pool.

They are following the lead of a U.S. Food and Drug Administration advisory panel's similar recommendation made last month. But not six months ago, both CBS and HQ asserted they would never impose such a ban since it would severely deplete the blood supply.

Have the CBS and HQ made a sound risk trade-off? The journal Nature noted that no cases of nvCJD "have ever been attributed to blood or a blood product since the new variant disease was identified." Dr. Adriano Aguzzi of Zurich University says "research has certainly not proven that blood is infectious." And a special council of the American Medical Association reported last month that "epidemiological studies show no evidence that transmission can occur through blood."

So is there any risk? If so, it is incredibly low: A little more than 40 people out of 50 million beef-eating Britons have demonstrated symptoms of the disease in question. Because of the uncertainty, we have no way of knowing if there are only a few more people incubating nvCJD, or if an entire beef-eating population is set to succumb. If mad cow lives up to its billing, these 40-some victims could just be the tip of the iceberg. However, Professor John Pattison, chairman of Britain's Spongiform Encephalopathy Committee, said last year that nvCJD should afflict only between 100 and 1,500 people -- making it a relatively small and contained health threat. With blood an unlikely infectious agent, the risk diminishes even more.

Because the proposed risk of nvCJD to the blood supply is theoretical, quantifying exactly who ought to be screened out is impossible. For instance, an American visiting Leicester for a weekend and consuming a couple of burgers, is he a threat? There is no tangible way to differentiate between him and someone who lived there for several years eating beef (such as myself). With Bovine Spongiform Encephalopathy nearly eliminated from the British landscape these days, when can we mark a cut-off point for the risk? As Portugal was recently thrashed for the spread of mad cow disease in its cattle, and British beef was consumed outside of Britain, should we perhaps ban donors who have been anywhere outside Canada?

The precautionary principle, invoked in this debate to countenance destroying a significant part of the blood cache, dictates that it is better to be safe than sorry. Unfortunately, risks do not exist in a vacuum -- they must be balanced. Rejecting one risk tends to present a half dozen other risks in its place. New donors could carry many other diseases more definitively risky -- including AIDS and hepatitis. But more importantly, finding replacement donors always proves difficult. Hence, our blood shortage. According to Richard Daly, chief medical officer for the American Red Cross, "It's likely . . . that taking this step in the face of a theoretical risk may actually decrease the safety of the blood supply."

This summer, Canada intends to begin leukoreduction -- the filtering of white blood cells. It could prevent the spread of nvCJD if the theory that it is caused by mis-shapen prions carried by white blood cells is correct. While expensive, leukoreduction has a wide range of other transfusion benefits, and ought to negate the need for any donor ban.

The capacity to spiral out of control in this odd worship of the precautionary principle threatens to do real harm to Canada. The Canadian Blood Services and Hema-Quebec face some hard questions. In particular, is no blood better than potentially bad blood?

Howard Fienberg is a research analyst with the Statistical Assessment Service in Washington, D.C.

 
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