I just went to donate blood. It was my first time, and no, Eclipse (vampires that twinkle in daylight? Please!!!) had nothing to do with it. I just thought it was the right thing to do, and someday I might need blood, and we're all in this together...motivations like that.
      Only, I was turned away. Seems my trip outside Chengdu in western China 11 months ago disqualified me. There was, in fact, a long list of things that disqualify a lot of potential donors. A couple of those disqualifiers raise some interesting risk perception questions, because they're based more on fear than scientific fact, and their net effect may actually raise the risk to the blood supply. It's a perfect example of what I call The Perception Gap, a gap between our fears and the facts that becomes a risk all by itself.
      Too few people donate blood. Shortages are chronic. Nonetheless, people who lived in the U.K for three months or more between 1980 and 1996, or who lived in other European countries for five years or more any time since 1980, are permanently banned from donating because of the fear of Mad Cow disease. There have been four cases in which blood is suspected of carrying the cow version of the disease, Bovine Spongiform Encephalopathy (BSE), to humans, causing the always-fatal variant Cruetzfeld-Jacob disease (vCJD). But scientists aren't sure that blood transfusions gave those four people the disease, of if they got vCJD the "normal" way, eating brain or spinal cord tissue from infected cows. And back when the world was really freaked out about BSE and vCJD, tests were done to see if blood could spread the disease. BSE-infected blood was injected directly into test animals, none of which got sick. Subsequent tests on sheep show blood may be a carrier. But even the British, where most of the rare Mad Cow disease cases occurred,  don't totally ban people who live there from donating blood. As a precaution, they remove white blood cells, which are thought to be the cells most at risk of carrying the disease in blood.
      But in the U.S., all those foreign travelers can't donate blood. Period. This despite the fact that such people make great donors. Foreign travelers are generally more affluent, and as a result generally healthier. They are also more likely to be repeat donors. and repeat donors are less likely to introduce dangerous infectious agents into the blood supply than new donors. But the "Mad Cow" ban reduced the blood supply by an estimated 10%. To make up for the drop in supply, the blood collection system needed new donors, who pose a greater risk of introducing germs that can spread disease through transfusion. Unlike BSE. D'OH!
      Here's another group that's out, for reasons based more on fear than fact. Any man or boy who had male-male sex, even once, back to 1977. Why? Fear of HIV/AIDS. Years ago there were cases of people getting HIV/AIDS from transfusions. Some died. But that was years ago, before we knew how to test blood to see who is HIV positive. Now, if you're a male who has tested negative for HIV but you have had gay sex, your blood is safe but you're out as a donor.
What's more, with DNA technology, we now can and DO screen all blood donations, looking for the genetic traces of not only HIV but many other dangerous germs, including other sexually transmitted diseases, or diseases spread when drug users share needles. We can find the ‘bad blood" and keep those donations out of the supply. This works. France, among many other countries, lifted the ban on donations from men who have had sex with men, and there have been no reported health problems.
      But the FDA in the U.S. recently decided to keep the ban in place. It's understandable. The people who get regular transfusions want every possible protection, including protection from sources of blood they fear, even if the evidence says they don't have to worry about those sources anymore. Those people are organized and lobby hard for bans like this, out of an understandable emotional concern. Most people...the people who might need blood in an emergency, and not get it because there is always a chronic shortage...don't make noise about these bans, and the shortages continue. The "Mad Cow" ban reduced the supply of blood by an estimated 1.4 million pints. The ban on gay men may be keeping more than 100,000 pints of blood from being donated per year.
      I really wanted to donate, and for a moment when the nurse showed me the map of China and pointed to the banned area and asked me if I had been there, I thought about lying. I didn't, and I was told my ban was only for 12 months, and to come back soon. But millions of people who want to give blood, and can...safely...are banned permanently, because when it comes to the perception of risk, it's not just about the facts, but also how those facts feel. the perceptions that result, as right as they feel, can leave us at greater risk.

The psychology of risk perception referred to above is described in detail in David Ropeik's new book, How Risky Is It, Really? Why Our Fears Don't Match the Facts.

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