standard question

This week at school I had to fill out a questionnaire for the PTA's newsletter. The questions included all of the ones I expected: name, nationality, birthday, hobbies, etc. The one that threw me for a loop was blood type. Why does the PTA want to know my blood type, and why would they put it in the newsletter? My Japanese teacher informed me that this is a very common question among Japanese people. Apparently they are very curious about blood type and it's a standard general-bio question. Random.