Today's interesting medical fact of the week is all about blood groups! Anyone who's done GCSE biology, or has donated blood (which you should do, incidentally) is probably aware that there are two most commonly used blood group systems. You're likely to be classed as Rhesus positive or negative - i.e. you either have, or do not have, a particular antigen on the surface of your blood cells - and then into one of the groups A, B, AB and O. People of blood type A react to blood with B antigens in, people with blood type B react to A antigens, people with blood type AB react to neither, and people with blood type O react all over the place, the whiners. Here is a handy chart from Wikipedia which explains it all clearly.
Apparently Back In The Day, kids used to routinely test their own blood group in school, thus gaining useful scientific understanding and practical skills. Unfortunately this practice was stopped, probably due to the dreaded Health and Safety, but (according to urban legend) also due to the fact that childrens' paternity kept being called into question by it.
Having given blood myself (after which I had a Funny Turn and was tragically forced to lie down eating biscuits for half an hour), I happen to know that my own blood type is A negative, which means that, were I to suffer significant blood loss, I could have a blood transfusion of either A negative or O negative blood. About 7% of the UK population is A negative- and about the same number have O- blood, so there's maybe 14% of blood stocks which would be available to me - probably a little less, because O- blood can be used for all blood types so it's used in emergencies where the recipient needs blood urgently and their blood group is unknown. So that's fine.
My parents admitted to me several years ago that there was a possibility we as a family could have moved to Hong Kong at one point in my childhood, which they mysteriously neglected to mention AT ALL at the time. Had we ended up moving to Hong Kong, our family's main concerns at the time would have been leaving behind all our family and friends, and not speaking the language. I doubt it would have occurred to anyone to even vaguely consider the fact that two of our family members have Rh negative blood. And in Hong Kong, and elsewhere in Asia, that is very, very rare. Only 0.69% of the population of Hong Kong are Rh negative. When your transfusion opportunities are restricted to A- and O-, only 0.5% of the population of possible blood donors are compatible.
I had no idea that this is actually a very real problem in Asia. There are numerous cases of people being unable to have treatment until donors of the right type are found, and if you suddenly lose blood in an emergency situation, things really don't look good. Because Caucasians have a much higher proportion of Rh negative people, foreigners often need to be targeted in blood drives.
It's also not something that I ever remember being informed about by anyone before travelling. The risk of needing a blood transfusion in other countries, if it's ever been mentioned to me, was framed as a risk of dirty or infected needles. One of the articles linked above, from a website for expats in Bali, notes that it's irresponsible for people to not know their blood type, and that all Rh negative expats should register to be put on a list of potential blood donors for emergency situations. It doesn't surprise me that people who travel out there aren't aware of this issue though, because I had never heard of it! And the problem is made worse by the fact that, due to vCJD ("mad cow disease") fears, many countries do not allow anyone who has lived in the UK or elsewhere in Europe to donate blood, further depleting the pool of possible donors.
So: be aware. And if you live in, or travel to Asia for an extended period of time, check out your blood type.
On a more lighthearted note: my favourite article from researching this post was a suggestion that people with RH negative blood are descended from aliens. Oh, and in Japan, blood types are used as we use star signs in the West, to categorise personality types.