But any Brit with a Japanese girlfriend or boyfriend will probably have faced that strange and slightly disturbing question and wondered for a moment whether they are being eyed up as a partner or a donor.
What lies behind this is the idea, popular in Japan, that people's blood type is indicative of their personality: so that Group O people, for example, might be creative, confident and optimistic, whilst Group A people might be shy, earnest and trustworthy. And what naturally follows on from this is the concept that certain blood types are more compatible with one group than another: so that O might be a good match for AB, but not for A. This kind of blood-type matchmaking is apparently very popular, especially amongst Japanese women.
As a result, pretty well everyone in Japan seems to know his or her blood type, much as most Westerners know their Zodiac sign, and I've found that some of my Japanese friends have been quite puzzled, or even shocked, when I tell them I don't know my own blood type.
How seriously this is taken obviously depends on the individual. In similar vein, I know people who believe every word of the horoscope they read in their daily newspaper. Japanese friends have sometimes asked me if I'm not just a bit curious about my blood group. Well, I suppose I could ask my doctor... but no, I'm quite content for him to keep that little secret to himself.